How to calculate the gestational age by the first movement of the fetus? Pregnancy terms: obstetric and embryonic - how to correctly determine the term

The gestation period for a woman is on average 38 weeks from the moment of conception. For most women, pregnancy lasts 266 days. But it is impossible to accurately calculate the date of future births until the day. Much depends on the hormonal background of the woman, concomitant diseases of the mother and fetus, the sex and weight of the unborn child, etc. But after 37 weeks of pregnancy, the fetus is ready for independent life (full-term). After this period, the born child is fully viable.

But a child after 42 weeks of pregnancy is considered, and childbirth can be accompanied by serious complications for the fetus. Therefore, it is important to know the gestational age not so much for the expected date of birth, but rather in order to know in what period the birth for a woman will be considered normal, and the child is full-term.

Pregnancy term obstetric and embryonic - differences

The obstetric gestation period is 40 weeks, and the embryonic one is only 38. It turns out a difference of 12-14 days. The obstetric period of pregnancy begins from the first day of the last menstruation. The embryonic period starts from the day of conception (from the day of ovulation, which usually occurs on the 14th day from the start of menstruation plus or minus 4 days).

How to calculate the obstetric gestational age?

The obstetric gestational age and the real (embryonic) differ by 2 weeks. In practice, the embryonic period is not considered and is limited to counting only obstetric. If a woman knows not only the start date of the last menstruation, but also the date of conception, then the embryonic lines of pregnancy are more accurate. The obstetric gestation period lasts 280 days from the first day of the last menstruation. According to the results of ultrasound, according to the tables, they confirm the compliance of the fetus with the obstetric, but not the embryonic gestational age.

Is it possible to calculate the date of birth according to the obstetric line of pregnancy?

The easiest way to calculate the expected date of birth can be considered as follows: from the first day of the last menstruation, add 280 days (Keller's formula). However, in practice it is difficult and the possible date of birth is determined by two similar methods.

1. Nine months and seven days are added to the start date of the last period.
2. Three months are subtracted from the start date of the last menstruation and seven days are added.

Obstetric weeks of pregnancy begin to count from the first day of the last menstruation. For the convenience of the doctor, 40 weeks are also divided into 3 trimesters. 1st trimester includes 1-14 weeks of pregnancy, 2nd trimester - 16-28 weeks, and 3rd trimester - from 29 to 40.

Obstetric gestational age and ultrasound

It is wrong to think that ultrasound determines the obstetric or embryonic gestational age. Rather, on the contrary, according to special tables, which include the average size of the fetus by obstetric weeks of pregnancy, they determine their compliance with the obstetric gestational age. Often the size of the fetus corresponds to the obstetric term plus or minus one week: the fetus develops normally. If the term according to ultrasound is less than the obstetric one, then this does not mean at all that the obstetric term was calculated incorrectly, rather something interferes with the normal development of the fetus. The main causes of intrauterine growth retardation of the fetus:

If the ultrasound term is longer than the obstetric one, then most often the cause will be the large weight of the unborn child (due to heredity, diabetes, overeating of the mother during pregnancy).

It is possible that the date of the last menstruation was determined by the woman incorrectly, and if she remembers the date, then it is better to recalculate the obstetric period through the embryonic period, adding two weeks to the last one.

As you know, in most cases, it is quite difficult for young girls to establish the exact date of conception. That is why in medical practice, when determining the duration of pregnancy, they always started from the date of the beginning of the last menstruation preceding pregnancy. With this calculation, the so-called "obstetric" gestational age is established, which is slightly longer and differs from the real one.

Many women who become pregnant for the first time do not know what the obstetric gestational age means and how to determine it. With a normal menstrual cycle (28 days), conception is possible on about day 14. Due to the fact that the date of the last menstruation is used in the calculation, the obstetric and embryonic (real) terms of pregnancy usually do not coincide. The run-up between them is the same 2 weeks, and sometimes 3.

How to calculate the embryonic (real) gestational age?

In order for a pregnant woman to independently calculate the actual gestational age, it is necessary to know the exact date of conception. If you can’t install it, then modern ones can come to the rescue. The design of such devices is based on electronic sensors that allow you to accurately determine the gestational age. The error in this case is small.

The situation is much easier when a woman remembers exactly the date of the last sexual contact. In this case, it is necessary to calculate only how many days have passed since that moment. The resulting number of weeks will be the actual gestational age.

According to statistics, the difference between the real and obstetric period of 2 weeks is observed only in 20% of pregnant women. For another 20%, the difference between these two terms is less than 14 days. In the majority, 45%, the difference between 2 terms varies in the range of 2-3 weeks, and only in 15% of pregnant women is more than 3 weeks.

If the average duration of a woman's menstrual cycle differs from the standard 28 days, then fertilization does not occur on day 14, but a little earlier or later. Therefore, the embryonic period will differ sharply from that established by the gynecologist.

For example, if a woman's cycle lasts 35 days, then conception can only occur on day 21, and not as usual - on day 14. Therefore, the embryonic gestation period at 1 week of delay will be 5 weeks. At the same time, if you count from the last menstruation, then it will already be 6 weeks.

In the early stages of pregnancy, it is possible to determine the period accurately enough only with the help of an analysis for. With its help, the approximate age of the fetus is established. In this case, the calculation is carried out from the date of the alleged conception. More accurately allows you to set the time of ultrasound. When conducting this study, the dimensions of individual parts of the fetal body are taken into account, according to which its age is established. According to the results of the ultrasound, it can be established as an obstetric gestational age, as well as embryonic.

When determining the gestational age, you can also take into account the duration of the cycle. Indeed, with a longer menstrual cycle, conception occurs a little later, therefore, childbirth will occur later.

Thus, knowing the main differences between the obstetric and embryonic gestational age, women will share these 2 concepts, and not be surprised that the period set by the gynecologist is longer than that expected by her, which is calculated according to the date of conception.