The gestation period for a woman is 38 weeks from the moment of conception. In most women, the pregnancy lasts 266 days. But it is impossible to calculate the date of future births until the day before. Much depends on the hormonal background of the woman, accompanying diseases of the mother and fetus, 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 completely viable.
But the child after 42 weeks of pregnancy is considered suffering , and labor can be accompanied by serious complications for the fetus. Therefore, the term of pregnancy is important to know not so much for the expected date of birth, but rather to know at what period the birth for a woman will be considered normal, and the child - full-term.
Term of pregnancy obstetric and fetal - differences
The obstetric period of pregnancy is 40 weeks, and the embryonic gestation period is 38. The difference is 12-14 days. Obstetrical gestation begins on the first day of the last month. The embryonic period starts from the day of conception (from the day of ovulation, which usually comes on day 14 from the start of the month plus or minus 4 days).
How to calculate obstetric pregnancy?
Obstetrical gestation and real (embryonic) pregnancy differ for 2 weeks. In practice, the embryonic period is not considered and is limited to counting only the obstetrician. If a woman knows not only the date of the onset of the last menstruation, but also the date of conception, then the embryonic lines of pregnancy are more accurate. Obstetrical gestation period lasts 280 days from the first day of the last month. According to the results of ultrasound, according to the tables, it is confirmed that the fetus corresponds to obstetric, but not embryonic, gestation.
Can I count the date of birth for the obstetric line of pregnancy?
The simplest way to calculate the expected date of birth can be considered the following: from the first day of the last monthly add 280 days (Keller's formula). However, in practice it is difficult and the possible date of birth is determined by two similar methods.
- By the start date of the last monthly period, nine months and seven days are added.
- From the date of the beginning of the last month, three months are taken and seven days are added.
Weeks from the first day of the last menstruation. For the convenience of the doctor, 40 weeks are still divided into 3 terms. 1 trimester includes 1-14 weeks of pregnancy, 2 trimester - 16-28 weeks, and 3 trimester - from 29 to 40.
Obstetrical gestation and the period of ultrasound
It is not correct to think that ultrasound is determined by obstetric or embryonic gestation. Rather, on the contrary, according to special tables, in which the average size of the fetus is made for obstetric pregnancy weeks, determine their compliance with obstetric pregnancy. Often the size of the fetus corresponds to the obstetric period plus minus one week: the fetus develops normally. If the term for ultrasound is less than obstetric, this does not mean that the obstetric term was incorrectly calculated, but something prevents the normal development of the fetus. The main causes of intrauterine growth retardation are:
- illness of the mother;
- violations of the normal functioning of the placenta;
- multiple pregnancies;
- chromosomal abnormalities of the fetus;
- intrauterine infections;
- bad habits of the mother;
- poor nutrition, etc.
If the term for ultrasound is more obstetric, then most often the cause will be the greater 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 of conception , it is better to count the obstetric period through embryonic, adding to the latter two weeks.