The childbirth in the human species , as in all mammals, can be defined as ” the expulsion of the fetus from the maternal genital organs at the end of pregnancy ” (Treccani, Dictionary of Medicine). It can occur due to a series of natural processes or through obstetric operations and, depending on the time of pregnancy in which it occurs, is considered a term, preterm (premature or early) or post-term (late).

Calculating the date of birth at the beginning of pregnancy is therefore very important because, when the long awaited moment arrives, it is possible to immediately understand if the child is punctual, early or late and to intervene in the most appropriate way.

But how is the estimated date of birth calculated? And how do we proceed in the event of a term delivery, premature or late because mother and child are not at risk?

Pregnancy and gestation: what’s the difference?

The dating of the pregnancy , therefore the calculation of the presumed date of birth, is based on a precise parameter, or the first day of the last menstruation : it would be complex to rely on the moment of conception (spermatozoa can survive inside the uterus until to five days), too uncertain to define.

Gestation and pregnancy , commonly used as synonyms, refer to two different concepts :

  • The gestation period is the period from conception to birth of the child ;
  • the pregnancy is the period from the first day of your last period until delivery .

The waste is in the two weeks from the first day of the last menstrual cycle, which coincides with the beginning of pregnancy, to the 14th day (ovulation phase in which conception takes place), from which the calculation is started of the weeks of gestation.

Expected date of birth: how is it calculated?

The calculation of the weeks of pregnancy is therefore based on the gestational age (calculated on the basis of the last menstruation) , not on the conceptional age (calculated on the basis of the moment of conception, which is assumed to be two weeks later). It is an important element to monitor the development of the embryo and to understand if the growth parameters are in the norm . It also allows the estimated date of birth to be calculated.

To do this it is necessary to count 280 days (40 weeks) from the first day of the last menstruation, with an extra margin or in less than 15 days . A pregnancy is “normal” if it ends 3 weeks before or two weeks after the fortieth. In this case, we talk about term delivery.

If, on the other hand, the pregnancy lasts less, or continues far beyond the term, the birth will be preterm or post-term. We must also specify that, especially when the woman has normally irregular cycles, it is important to perform a date with an ultrasound scan at the beginning of pregnancy: measuring the length of the embryo is, in fact, the most reliable means of dating pregnancy.