How to calculate the gestational age for the last menstruation. Methods for determining the term in the early stages of pregnancy

One day for every expectant mother comes that very special day. She learns about her new condition. And soon a woman will often hear the question: “What is your (your) deadline?” How to calculate the gestational age to answer correctly?

It's pretty simple!

Almost always, the answer to the question about the gestational age will be based on the two most famous and popular calculation methods - obstetric and embryonic (from conception) terms.

obstetric term

The beginning of pregnancy is the first day of the last menstruation. This method is called obstetric. It does not take into account the individual characteristics of the woman's body, but is almost universal. Any doctor will use it.

The obstetric method has its own logic. The term is calculated from the earliest stage of pregnancy - the beginning of egg maturation.

Using the obstetric method, the doctor will determine the expected date of birth (PDR), as well as the period of maternity leave. In medicine, it is generally accepted that pregnancy lasts 280 days. This is the well-known 40 weeks or 10 lunar months.

Why 10 months and not 9? And why are the months lunar? Astronomy is to blame for this. The moon repeats its phases at intervals of 28 days (4 weeks). This is the lunar month. And if you count in calendar months, then only 9 of them really fit in a normal pregnancy.

Embryonic (true) term - from conception

The beginning of pregnancy is the first day of the last menstruation plus 2 weeks. It is believed that it is in the middle of the cycle that ovulation occurs. In this case, the period from one month to another is taken as an average - 28 days.

This method of calculating the term is called embryonic or true. But it’s worth considering: isn’t the truth hiding somewhere else? From a medical point of view, ovulation can occur within 12-18 days from the start of the cycle.

Example. Oksana's husband from the beginning of spring until late autumn constantly traveled on business trips. At home I was sometimes only one or two days a month. Soon after another visit by her husband, Oksana realized that she was pregnant. And with a smile, I thought that I knew the exact date of conception - June 2. After all, before and after that day, she and her husband did not see each other for almost two weeks. Oksana's last period was May 18-21. And if we consider May 22 as the beginning of the cycle, then the conception took place on the twelfth day. And the egg was already mature. Or not?

Another question is important here - how long does ovulation last? If strictly according to science, then a few seconds. After all, ovulation is only the release of a mature egg from the follicle. But most of us consider ovulation to be the next few (or even many) hours that the egg will live in the female body. How many? Sometimes up to two days. By the way, about the same amount will live in the female body and sperm after intercourse. And sometimes even longer - up to a week.

So the true day of conception is a real mystery! After all, there may well be two different situations. The egg moves to the uterus for the second day and literally at the end of its life it turns out to be fertilized. Or vice versa. Spermatozoa entered the woman's body before ovulation and actually "waited" for the release of the egg.

As accurately as possible, the day of conception is known to couples who carefully planned their pregnancy. In this case, the day of ovulation is determined using a special test (sold in a pharmacy) or by ultrasound.

There is another old method for determining ovulation. This is a measurement of basal temperature. It is carried out in the morning, at the same time, before getting out of bed (it is even recommended not to open your eyes). The thermometer is placed in the mouth, vagina or rectum. Before ovulation, basal body temperature drops slightly and then rises. This means the release of a mature egg.

And sometimes women themselves feel that ovulation has come. The lower abdomen aches, the discharge from the vagina becomes a little more viscous. And the attraction to the beloved man becomes stronger.

That is why many expectant mothers consider their gestational age to be the embryonic method: the beginning of the cycle plus 2 weeks or the day of ovulation known to them. In this case, we are talking about the period from conception.

Can there be difficulties?

Lyudmila's periods often came literally "every other time." The doctor's verdict is ovarian dysfunction. While Luda did not live a sexual life, she did not worry too much. But after marriage, the same question often came. Delay is a sign of dysfunction? Or the contraception didn't work? Once the second option turned out to be correct. But the doctors could not calculate the term by the usual method - there was a clear discrepancy.
For the former athlete Valeria, the first menstruation came only at the age of 16. And the cycle was not established in any way. Up to six months could pass between critical days. The girl did not go to the doctor. I somehow didn’t find time - either study, or personal life. One day, thin Valeria noticed that she had clearly gained weight. The first reaction is the desire to go on a strict diet and remember the previous sports loads. It's good that the girl first consulted with her mother. More precisely, with the future grandmother of her child.
Lena's first child had just turned ten months old. The baby grew up healthy, and on the occasion of such a round date, the nursing mother decided to eat melon. A few hours later, she became nauseous. Lena thought she was poisoned. But soon the doctors clarified the situation: Lena was pregnant again. The first period after childbirth simply did not have time to begin.

How many more such cases! If a woman's periods are irregular or did not have time to come at all, as in the situation with Lena, traditional calculations will not help. It's good that there are alternative methods.

How else to determine the time?

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based on a gynecological examination;
with the help of ultrasound;
by the first movement of the fetus;
according to the size of the uterus.

In some cases, the doctor "looks after" all the signs in order to make less mistakes in calculating the term.

Gynecological examination

An experienced gynecologist will be able to calculate the correct period only by the size of the uterus. The doctor's hands will accurately determine the boundaries of the uterine cavity. If the uterus is comparable in size to a chicken egg, the period is 4 weeks. And if closer to the goose, then we are talking about eight weeks.

This method works effectively if the gestational age is less than 12 weeks.

ultrasound

Ultrasound scanning today allows you to effectively examine the fetus and even take some measurements. In the first trimester, the doctor will determine the size of the fetal egg and compare them with traditional data. In the second and third, the doctor will already measure the circumference of the chest, tummy or head. The last "measure" is considered the most correct for determining the term.

In the first weeks of pregnancy, calculating the term in this way gives a very accurate result. Later, future babies begin to differ greatly: some are larger, some are smaller. Just like in the life that awaits them in the future.

Baby is pushing!

The first fetal movement is another indicator. If a woman is preparing to give birth to her first child, she will feel his movements at 20 weeks. If the baby is the second, third, and so on, then the first stirring is expected at 18 weeks. This is official medical data. And future kids do not at all consider that they must follow them!

The fetus actually makes its first movements in the first trimester of pregnancy. But the unborn child is still so tiny that the mother does not feel anything for many weeks. But there are exceptions.

Inna was expecting her second child. And so she was thin, and in the first weeks she even lost weight. With a height of 167 cm - 46 kg. And this is in the second trimester! The doctor shook his head disapprovingly and worried. And Inna felt great. Nausea almost did not torment, vomiting was occasionally. True, I constantly wanted oranges, and one red-haired “handsome man” was always in my bag. And there were no problems at all.
The baby pushed at the seventeenth week. First once, and after a couple of hours - again. And the next day, and the day after, the woman experienced the same sensations. At the next appointment with the gynecologist, Inna named the date. The doctor once again shook her head, smiled and clarified - maybe it was gases? Inna laughed - she perfectly remembered the movements of the baby from her first pregnancy and could not be mistaken.

True, sometimes you can still confuse. If the expectant mother regularly suffers from flatulence, and even expects a child for the first time, the movement of gas through the intestines is sometimes taken by her for the movements of the baby.

When weeks equal centimeters

And another way, which is related to the size of the uterus. More precisely, with its height. This method is available only to doctors. The pregnant woman lies down on the couch. The doctor takes a centimeter tape or a special tool - a pelvis meter. Determines the upper and lower boundaries of the uterine cavity and makes measurements.

The height of the uterus in centimeters is the gestational age. That is, if the doctor measures 30 cm, then the gestational age is 30 weeks.

These four methods (usually in combination with each other) give the most accurate determination of the gestational age.

And when will it be born?

The expected date of birth will tell the mother when the baby will be born. But this is a theory. Children very rarely follow the calculations of doctors. True, there are exceptions here.

On ultrasound at 12 weeks, Lika was called PDR - March 10. Lika just shrugged her shoulders. She carried her first baby exactly a week. The doctors then said that the baby probably wants to grow up. Indeed, even a post-term son weighed only 2 kg 700 g at birth.
Therefore, early in the morning on March 10, Lika did not even immediately realize that contractions had begun, and stubbornly tried to sleep a little more. But it didn't work out. It soon became clear - it began. That's how the daughter was born - just right on time.

Negele formula:

Quite accurately, the expectant mother can calculate the EDD herself. Of course, if the periods before conception were regular.

It is necessary to add seven more days to the first day of the last menstruation, and then subtract three months.
Or add 9 months and 7 days to the first day of your last period.

Here is the approximate date of birth of the future crumbs!

You can find out the EDD using a special pregnancy calendar for the last menstruation. In the red line we are looking for the date of the beginning of the last menstruation, next to it, in the yellow line, we see the date of the probable day of delivery.

For example, the last menstruation began on January 28. Plus seven days is February 4th. Minus three months - we get the 4th of November. And how it will actually be - life will show.

The main thing is that at any time the pregnancy should be easy.

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A woman, having learned from a doctor about her desired pregnancy, will definitely want to find out the “age” of the future crumbs. There are several ways to determine the date of birth of the baby, both independent and with the help of specialists. How to correctly calculate the gestational age, as well as how the real term differs from the obstetric one, we will try to tell in this article.

The obstetric term, which is set by gynecologists at the first appointment with the expectant mother, differs markedly from the real one, but is the most accurate parameter. It is believed that pregnancy occurs at the moment of direct conception or fertilization of the mother's egg. This usually happens around the middle of the menstrual cycle, so if a woman knows the day when the egg leaves the follicle and ovulation begins, then she can accurately calculate the gestational age.

Basal body temperature (BT)

To do this, you need to daily, remaining in a horizontal position in bed, measure the temperature by the rectal method. After menstruation, in the period of 10-14 days, it most often does not exceed 37 degrees, and during and after ovulation, it can rise to 37.2-37.3 degrees. The day of conception does not always coincide with the time of sexual intercourse. The sperm cell has the ability to survive from three to seven days in anticipation of the appearance of the egg from the ovary. And the lifespan of the mother cell itself is limited to 24 hours. Therefore, if sexual intercourse occurred 5-7 days earlier than ovulation occurred, then conception can occur 5-7 days later than coitus. Therefore, experts argue that this method of counting for determining the embryonic period is not entirely accurate. In addition, each woman, due to her individual characteristics: a certain menstrual cycle, the day of ovulation and the possibility of re-emerging the egg from the ovaries, will have her own developmental period of the fetus, which cannot be determined one hundred percent.

In obstetric practice, the date of the first day of the last menstruation is used. The error of this method is only 7-14 days. The obstetric period is calculated in two ways: 10 average menstrual cycles (28x10) or 280 days are added to the first day of the last menstruation; in the second case, 3 months are subtracted from the same date and 7 days are added (Negele's formula). In the ideal case, when the exact date of ovulation is known (days 12-16 of the menstrual cycle), 264 days can be added.

Note! At the appointment with the gynecologist, the expectant mother will find out the obstetric period, since doctors do not take into account the rest of the calculations.

Ultrasonography

For many years, the ultrasound method has been quite actively used in the diagnosis of fetal development. The most accurate gestational age is obtained using studies conducted at the earliest stage of pregnancy - up to 8 weeks. The development of healthy embryos these days is identical and it is possible to determine the gestational age up to a day by the size of the fetus. In the future, the children begin to show their individuality, any healthy fetus may have minor deviations (for example, growth is slightly below normal or the size of the head is slightly larger). If this difference fits within a period of no more than 7-10 days, then doctors usually do not take this circumstance into account, but if it is a period of two or more weeks, then doctors diagnose intrauterine growth retardation and recommend paying attention to proper balanced nutrition , walks, a healthy lifestyle that will help normalize the development of the embryo.

A gynecologist's consultation on the first day of pregnancy delay is usually not needed, since the doctor will not yet be able to determine whether the uterus is enlarged as a result of PMS or conception. The perceptible growth of this female organ in connection with pregnancy begins only at the end of the first trimester. In the second or third week of delayed menstruation (for a period of 5-6 weeks), the uterus reaches the size of a chicken egg, at 8 weeks - a goose, at 10 - usually acquires the size of a female fist.

HCG and gestational age

How to correctly calculate the gestational age using human chorionic gonadotropin? Ideally, a blood test from a vein is not used to determine the timing of an “interesting situation”, but for the early diagnosis of possible complications. In the second week, an approximate table of hCG values in the blood of a pregnant woman contains a parameter from 25 to 150 IU per ml, and in the eighth - up to 70 thousand IU per ml. Serious deviations from the table values indicate a serious pathology, such as missed or ectopic pregnancy.

First fetal movement

Doctors say that in first-time pregnant women, the feeling of the inner presence of the baby occurs exactly at 20 weeks of pregnancy, in re-pregnant women - at 18 weeks. This date is an important step in the correct calculation of the gestational age. It is easy to notice the movement, especially when lying on your back.

Uterine length

Starting from the second trimester of pregnancy, gynecologists measure the length of the uterus with a centimeter tape in the patient lying on the couch. In a future mother, the uterus adds about a centimeter in size every week. In addition, there are special tables that can be found in manuals on gynecology and obstetrics.

Heart tones

The embryo's heart begins to beat already at four and a half weeks (or 2-3 weeks after a woman's period is missed). This is noticeable in early ultrasound examinations. Through an obstetric stethoscope, the fetal heartbeat is heard much later, approximately after the date of the beginning of the movement of the future crumbs. Poor hearing can be caused by a placenta located closer to the anterior wall of the uterus or significant abdominal deposits of adipose tissue.

No matter how hard you try to correctly calculate the gestational age to the day, most likely it is unlikely to succeed. This can only be done hypothetically. Your baby will be born into the world only according to the laws of Mother Nature, when he is ready for this. Good luck in this difficult and noble cause!

Video

You can learn more about calculating the gestational age from the following video:

Each representative of the fair sex, having learned that she is in a position, seeks to calculate the exact gestational age as soon as possible. According to it, you can calculate the approximate date of birth of the long-awaited baby. Determination of the gestational age is also required by the gynecologist to track the development of the fetus, identify violations, and timely prescribe tests and examinations.

How do doctors determine the duration of pregnancy?

For women who come to a medical facility and claim to be pregnant, the gynecologist first of all asks when the last menstruation was. It is from this date that he will count. Interesting, right? Fertilization has not yet come, since it occurs during ovulation in the middle of the cycle, and obstetricians start counting from such an early date.

This method of determining the duration of pregnancy and childbirth is called " obstetric». True the period of an interesting position is about 2 weeks less than the period that the doctor tells the pregnant woman. The minimum period for determining pregnancy by this method is 2-3 weeks.

You can find out the period by the results of ultrasound. Their accuracy will be less in the later stages, because each baby develops in the mother's tummy in its own way. The doctor determines the gestational age by the size of the fetus. The following indicators are measured:

biparietal size, determined between the temporal bones (BDP);
fronto-occipital size (LZR);
head circumference (OG);
abdominal circumference (OC);
thigh length (DLB);
chest diameter (DRD), etc.

Each week is characterized by certain values of the above criteria. The gynecologist uses a special table for determining the timing of pregnancy to calculate.

The doctor can determine the term of an interesting position by the size of the uterus during a gynecological examination. For example, at the 4th week of pregnancy, the organ can be compared with a chicken egg, and at the 8th week - with a goose egg. Later, it is difficult to establish the term according to the size of the uterus.

How else do doctors determine the duration of pregnancy? For example, a method is used to determine the duration of the position along the length of the uterus. A tazomer or centimeter tape is used. As a rule, the number of weeks is equal to the length of the uterus. For example, during the measurement, it turned out that the length of the uterus is 34 cm. This means that the period is 34 weeks. To obtain reliable results, a woman is advised to empty her bladder before visiting a doctor.

How to determine the gestational age at home?

A pregnant woman can independently calculate the duration of her interesting position without the help of doctors. How to find out the gestational age at home? There are several ways:

according to the last menstruation;
by date of conception
at the first stirring of the crumbs;
using an online calculator.

1. How to determine the gestational age by the last menstruation?

The easiest way that doctors and many women find out the gestational age is by the last menstruation. How to determine the most gestational age by the last menstruation? Between the date of the beginning of menstruation and the date of the calculation, it is necessary to calculate the number of weeks. This will be the duration of the pregnancy.

By the date of the last menstruation, it is convenient to calculate the date of birth. There is a special Nagel formula. From the date of the last menstruation, 3 months are counted back and 7 days are added.

The calculation of pregnancy by the last menstruation is a fairly simple, but inaccurate method, since it is a couple of weeks longer than the true period.

2. How to determine the gestational age by the date of conception?

Recall that conception occurs approximately in the middle of the cycle after the release of a mature egg from the ovary (ovulation) during the day. The method of calculating the gestational age by the date of conception is suitable for those women who know exactly when they ovulated. The gestational age is determined by weeks. The countdown is from the date of ovulation. Average values can also be used (for example, with a 28-day cycle, ovulation approximately occurs on day 14, i.e., in the middle of the cycle). And how to determine the gestational age with an irregular cycle? In such cases, approximate values \u200b\u200bare not suitable.

The moment of release of an egg ready for fertilization can be determined using special tests, basal temperature or ultrasound results. Some women determine ovulation by how they feel (by the presence of pain in the lower abdomen, abundant discharge from the penis, increased libido). If the date of ovulation (and, accordingly, the date of conception) is unknown, then using the method of determining the gestational age by the date of conception will not work, since the results will not be accurate.

3. How to determine the gestational age by the first movement?

The baby begins to move in the tummy of the mother, whose pregnancy is the first, from the 20th week. Multiparous women begin to feel movements from the 18th week.

It is worth noting that using this method it is not always possible to find out the exact time. Some women feel the first movements much earlier than the indicated weeks, and some vice versa later. Most doctors note that the fair sex often confuses the first movements with the "work" of the intestines, because it is known that many pregnant women suffer from increased gas formation.

4. How to determine the gestational age using a calculator?

To calculate the gestational age, you can use the calculator, which is presented below. His work is based on the method of determining the period by the last menstruation, which was described above. How to determine the gestational age using an online calculator? In order to use it, you need to know the date of the beginning of the last menstruation, the average duration of the menstrual cycle and the luteal phase. The results of the calculation will be known immediately.

Summing up all of the above, I would like to note that many women are interested in the question of how to accurately determine the gestational age. However, with almost all of the above methods, it can not be calculated accurately. The only exceptions are cases when a pregnant woman knows the exact day of ovulation. Is it necessary to know the absolutely exact term of an interesting position? It is worth noting that it is not so important. Deviations of a few days or a week will not play a big role, so do not be afraid if the exact day of ovulation and conception is not known.

Answers

Pregnancy is a long-awaited moment in a woman's life. From the moment of conception, the expectant mother already wants to know the date of birth of her baby.

Everything here is not always clear and unambiguous. For example, here is one of the questions I receive daily:

“Tell me, please, I’m pregnant, according to my monthly period I should give birth on September 24, according to ultrasound at 18 weeks, they set the date for October 16, the second ultrasound at 33 weeks is set for October 11. But when I was filling out the documents for the maternity hospital, they sent me for another ultrasound, and it showed September 30th. How can this be and what should I do, go to save now or wait until it grabs? Thanks in advance".

How to accurately determine the gestational age?

Different methods are used to determine the gestational age and date of birth.

Determining the gestational age and date of delivery by the date of the last menstruation

Usually the first thing the gynecologist asks at the appointment is the date of the last one.

In obstetrics and gynecology, the cyclicity and regularity of menstruation is an indicator of a woman's health.

In order to track the regularity of menstruation, a woman needs to keep her .

The most common way to determine the date of birth is the method by the date of the last menstruation.

The starting point is taken first day last menstruation. 40 weeks or 280 days or 9 calendar months or 10 lunar months are counted from this day - this will be the approximate date of birth.

The date of birth by this method is still determined according to the Negele formula: from the first day of the last menstruation, it is necessary to count 3 months ago and add 7 days to this date. This will be the date of the expected birth.

For example, the first day of menstruation was October 1st. We count back 3 months from this date (September 1, August 1, July 1 and add 7). It turns out July 8 - the estimated date of birth.

ATTENTION! This is only the estimated date of birth, because. many women give birth a little earlier or later than this date.

What does it depend on? From many factors. From the course of pregnancy itself, from the maturity of the child, from the readiness of the mother's body for childbirth, from diseases that aggravate pregnancy.

Determination of the term of childbirth by the date of ovulation

Determining the gestational age and date of birth by ovulation is more accurate. From the date of ovulation, count the past weeks - this will be the gestational age by the date of ovulation.

If you know the day of your ovulation, then add 273-274 days to this date and get the estimated date of birth.

Determining the due date by the date of conception

This is a more accurate way if you know for sure date of conception or sexual intercourse, especially if it was the only one. From the moment of conception to the moment of birth, 266 days must pass.

Add 266 to the date of conception and you get the estimated date of birth. It will also be approximate, because exactly day of conception hard to know.

What other ways are there to determine the gestational age?

Determining the gestational age by ultrasound

From the moment the ovum is immersed in the uterine cavity, with the help of an ultrasound machine, it is already possible to see signs of pregnancy. They are determined by the size of the uterus, by the size of the fetal egg, by the size of the embryo. At later dates - along the length of the thigh, the length of the shoulder, the size of the head and abdomen of the child, the thickness of the placenta.

There are special tables according to which the doctor calculates the gestational age by comparing the data obtained.

Determination of the gestational age by the height of the fundus of the uterus (VDM)

At later dates, starting from 14-16 weeks, the uterus comes out of the small pelvis and is already palpable above the woman's bosom. The doctor measures the height of the uterine fundus with a centimeter tape.

As a rule of thumb, WMD in centimeters = gestational age in weeks. For example, WDM = 16cm, which means that according to WDM, a woman is 16 weeks pregnant.

Determination of the gestational age by gynecological examination

Examination by a gynecologist is one of the accurate methods for determining the duration of pregnancy. Normally, the uterus has dimensions of 3x4x5 cm. During pregnancy, the uterus increases in size, becomes rounded, soft, and its anterior-posterior size increases.

When setting the gestational age, the gynecologist focuses on the size of the uterus. They are measured in weeks of pregnancy. For example, uterus the size of a newborn's head- This is 12-13 weeks of pregnancy.

Determination of the term of childbirth by the first movement

The primiparous woman begins to feel the movement of the child from the 20th week of pregnancy, and the multiparous - from the 18th week.

The doctor will ask you to remember the date of the first movement. From this date, 20 weeks are counted for primiparous and 22 weeks for multiparous and an approximate date of birth is obtained.

Sometimes women begin to feel a stir from an earlier date. For example, from 15 weeks. But in this case, the calculation of the date of birth will be very inaccurate.

In practice, to determine the gestational age and due date, the doctor will use ALL of these methods.

If there is a discrepancy between the size of the child and the gestational age, then this means signs of intrauterine growth retardation of the fetus and requires special treatment.

Thus, in order to establish the correct gestational age and determine the date of birth, a lot of calculations, measurements, and calculations are required.

Currently, the date of birth is very often determined by the doctors themselves or pregnant women when they decide that the pregnancy should end with a caesarean section, but more on that next time.

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Every woman, having learned that she will soon become a mother, wants to understand when the first meeting with the baby will take place. To do this, you need to find out the gestational age, you can calculate it in several ways.

But even the most accurate calculations will only give, because not every pregnancy lasts exactly 40 weeks. Approximate terms are set by the doctor when registering and within 9 months can be slightly adjusted.

Ways to determine the duration of pregnancy

You can calculate the gestational age in different ways. Each has its pros and cons. Some calculations are easy to do at home on your own, armed with a calendar, other methods of determining the due date require the help of a doctor and medical equipment.

By date of ovulation (conception)

This counting method is the most accurate, especially in the early stages. Conception can only occur during a period that lasts several hours, and over the next day, while the egg remains in the fallopian tube. If the spermatozoa enter the uterus later, then fertilization is no longer possible.

There are three ways to determine the day on which ovulation occurred:

Calendar . Most often, menstruation begins exactly 2 weeks after ovulation. Knowing the duration, you can calculate the day when the egg left the ovary and was in the fallopian tube - the period of conception. For example, if 30 days pass from the beginning of one period to the beginning of others, then the calculation of ovulation will be as follows: 30-14 = 16 (conception occurred on the 16-17th day of the cycle). But this method turns out to be inappropriate in cases where ovulation or, that is, occurs not after 14 days, but after 10-13 or 15-18. Such a calculation will also fail to be performed by women with.
. The principle of operation of this test is based on the detection of high levels of luteinizing hormone in urine or saliva. Its amount varies throughout the cycle and reaches a maximum on the eve of ovulation. When the test gives, it means that conception can occur in the next 24-48 hours. Pharmacies can be purchased, which react to the concentration of luteinizing hormone in saliva. They are designed for one or more applications. A more common option is strip strips that determine the level of LH in the urine.
Schedule . This method requires a long measurement of temperature in the rectum. The procedure should be done in the morning without getting out of bed. Record all data daily. Ovulation on the chart will be determined by a sharp increase in values by 0.4-0.6 degrees. In the first half of the cycle, it is not more than 37 ° C, on the day the egg is released from the ovary, it increases and stays at about the same level until the next menstruation. The disadvantage of this method is that such changes may not be caused by ovulation, but, for example, by a recent sexual intercourse or a cold that begins.

Do not confuse the day of sexual intercourse and the day of conception. Fertilization of the egg is possible within 24-36 hours after ovulation. Spermatozoa, entering the body of a woman, can remain alive for up to 7 days. That is, within a week (usually 3-5 days) after intercourse, conception can occur.

By the date of the beginning of the menstrual cycle

This is how the obstetric gestational age is calculated. It does not take into account on which day the conception occurred and the development of the embryo began. Therefore, it is not entirely accurate, the error can be from 7 to 14 days.

How to calculate the gestational age by the last menstruation? First you need to remember when they started. For further calculations, it is better to prepare a calendar. It is necessary to determine the number of days from the first day of the last menstrual bleeding to today. This will be the obstetric gestational age.

You can find out the expected time of birth of a child in the following ways:

From the beginning of the last menstruation, count 40 weeks.
From the beginning of the last menstruation, subtract (count back) 3 months, and then add 1 week. Move this calendar date forward one year.

For example, a woman's last period began on October 20, 2016. According to method 1, we add 40 weeks, we get the expected date of birth - July 27, 2017. We calculate in 2 ways: October 20 minus 3 months - July 20, plus 1 week - July 27. The dates match, both calculations are correct.

This method of calculation is most accurate for women with a 28-day menstrual cycle. How to make it easier - to correctly calculate the gestational age, an online calculator will help, but again, only for the reference cycle. In other cases, a doctor can confirm the date more reliably.

By date of first movement

The method of determining the date of birth by the first movement has been used for over 100 years. It was very relevant at a time when medical technology and knowledge were not developed. Now doctors do not use it, since in other ways it is possible to calculate the gestational age in weeks more accurately.

It is believed that the first stirring occurs exactly in the middle of pregnancy. Based on this, you can calculate the expected date of birth. Embryonic development of the fetus lasts 38 weeks. So, by the day when the woman felt the first tremors, you need to add 19 weeks - this will be the expected date of birth. And if we subtract the same period of time, we get the date of conception.

But the error of such a calculation is very large:

With the help of modern medical equipment, it has been established that the baby can begin to move as early as the 12th week of pregnancy, but women feel it later.
Most often, women who will give birth for the first time begin to feel the baby's movements at week 20, and those who already have children, early at 18. It turns out that the calculations for the date of birth will be as follows: we add 18 weeks to the day of the first movement (for those who have a first pregnancy) or 20 weeks (for repeated pregnancies).
All women have different sensitivities. According to the observations of doctors, lean women leading a sedentary lifestyle are the first to determine movements. They celebrate them as early as the 14th week of pregnancy.

Given that the pregnancy itself can take from 38 to 42 weeks, the error in this calculation becomes even greater. Doctors mark the day of the first movement on the chart, but it is not used to adjust the estimated date of birth.

According to measurements of the uterus

From a certain period, namely from 6 months, the height of the uterine fundus in centimeters corresponds to the number of weeks of gestation. Therefore, by measuring this parameter, you can calculate the approximate date of birth and gestational age.

The standing height of the bottom of the uterus is the distance from its upper edge to the pubic joint. The gynecologist measures it from 14-16 weeks, before this period it is located behind the pubic bone, and you can find out its dimensions only during a vaginal examination.

Of the tools you need only a centimeter tape. You need to lie on your back, after emptying your bladder. Release the belly from clothes and carefully feel it along the lobar line: in the place where the elastic belly becomes soft, the bottom of the uterus (its upper border) is located. You need to measure from this point to the pubic joint.

To make it easier to find the upper border of the uterus, you can focus on the standard indicators:

at week 12, it reaches the upper edge of the pubic bone, the size of the entire uterus is comparable to the size of the head of a newborn child, it is still impossible to probe and measure it;
at week 16 - located 6 cm from the pubic joint, you need to feel the distance from the navel to the pubic bone;
20 - 12 cm above the womb, determined approximately 2 fingers below the navel;
at 24 - palpable at 22-24 cm from the pubis, just in the navel area;
28 - 27-29 cm, which is about 2-3 fingers above the navel;
at 32 - it is installed 31-33 cm from the womb, palpated between the navel and the beginning of the sternum approximately in the middle;
at 36 - 35-37 cm, determined at the level of the beginning of the sternum;
at 40 weeks, the child places the head in the pelvic bones, and the uterus descends slightly, the height of its bottom is 32-33 cm, it is palpable between the navel and the beginning of the sternum.

How to calculate what the exact gestational age is now and when the birth will occur, knowing the height of the uterine fundus? This can be done when the indicator reaches 24 cm. From this period, the number of weeks of pregnancy is the same (24 or more). Considering that the entire pregnancy lasts 40 weeks, the calculations are easy to make.

The accuracy of this method is not high, so at present it is practically not used. But these measurements are still carried out, their purpose is to identify possible complications. If the height of the uterine fundus does not correspond to the gestational age, this may be a sign of cystic drift, tumors and other pathologies.

ultrasound

Ultrasound can be performed early. Already from 3-5 weeks, the fetal egg begins to be visualized, determining its location helps to exclude, and the diameter - to set the period.

At 5-6 weeks, the embryo itself is viewed, the doctor measures the coccyx-parietal size (). There are normative values of this indicator for certain periods. From the comparison, the gestational age and the approximate date of delivery are calculated.

In the 2nd and 3rd trimesters during ultrasound, the following indicators are measured:

biparietal size - the segment between the parietal tubercles;
circumference of the head, chest and abdomen;
thigh bone length.

For all these values, there are also norms. By comparing the measurement values, the gestational age can be calculated and the date of delivery can be estimated. But as individual differences become more apparent every week, the probability of error is constantly growing. The size of the fetus reflects the disease of the mother, hereditary factors, especially the course of pregnancy. Therefore, by the end of gestation, a child can weigh 2700 grams or 4500 - both options will be the norm.

So, determining the duration of pregnancy and the date of birth using ultrasound will be accurate up to 12 weeks. The more time has passed since this period, the less reliable the results will be.

According to the level of hCG

Human chorionic gonadotropin is a hormone that is produced by the fetal membranes from the 6th day after conception. The first weeks there is a rapid increase in its concentration in the blood: twice every 2 days. Then its production gradually decreases, and from 9-11 weeks the indicators begin to decrease.

You can find out the concentration of hCG in the blood by passing it for laboratory analysis. There are certain norms for the content of this hormone in plasma for a certain period of pregnancy. Each laboratory uses its own reagents, the sensitivity of which is different. Therefore, there is no single table of standard values.

The method of determining the gestational age by the level of hCG in the blood is practically not used, although it is quite accurate, especially in the early stages. The analysis is carried out to detect pathologies, for example, or implantation of the embryo outside the uterine cavity.

What difficulties may arise?

No matter how accurate the methods for calculating the duration of pregnancy, they all give only an approximate date of birth. It is impossible to say with a 100% guarantee when the baby will be born.

According to statistics, 17% of pregnant women give birth on the day expected by doctors, and the remaining majority - sooner or later. It turns out that even the most qualified specialists and high-tech equipment are not able to perform an absolutely accurate calculation.

Normal labor is considered to begin between 38 and 42 weeks of gestation. In these cases, the fetus is considered full-term. With some complications, labor begins. The cause may be the pathology of the development of the child, stressful situations, various disorders in the mother's body, hereditary factors. All this must be taken into account when calculating the gestational age.

The child is often observed when, in the case of taking hormonal drugs, with impaired ovarian function. The hereditary factor also influences: if there have been late births along the female line, then it is likely that they will be repeated.

The menstrual cycle and ovulation are physiological processes. The cycle length ranges from 24 to 35 days. Therefore, any calculations based on them will always have a certain amount of error.

Standard calculations are based on the assumption that pregnancy lasts 40 weeks, and this is only true for a 28-day cycle. The time of ovulation is also determined by static data: 14 days before the onset of menstruation. In fact, this process can happen 3-4 days earlier or later.

You can calculate the gestational age in different ways. The most accurate are the determination by the date of conception (ovulation), by the last day of menstruation and according to ultrasound data for up to 12 weeks. Other methods can be considered auxiliary, they allow a large share of the error and for this purpose are not used in medical practice.

Even the most accurate method can be wrong by 1-2 weeks, or even more. This is due to the fact that the duration of bearing a child ranges from 38 to 42 weeks (normal), the menstrual cycle - from 24 to 35 days, the onset of ovulation can also occur a few days earlier or later than expected in standard calculations.

Useful video on how to calculate the gestational age and due date

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