Definition of pregnancy and its phases

Pregnancies date from first day of the last period and the probable date of delivery is calculated 40 weeks later. According to these accounts, a initial period, which in women with regular cycles is two weeks, in which the woman is not yet pregnant, but usually the date of last menstruation It is the only data available to date the pregnancy. In the cases in which we know the date of conception, it would be Add 38 weeks to that date.

Pregnancy is also divided by quarters, because each of them has its different connotations:

The first trimester

The first 3 months or counting in weeks from conception to week 13-14, is the one with the highest risk of pregnancy loss, spontaneous abortions that are frequent in this trimester as they are pregnancies resulting from embryos with some chromosomal or anatomical defect that does not allow it to continue developing normally beyond the first weeks.

It is the period in which all fetal organs will be formed, which will be complete at the end of this quarter.

We also associate it with the most uncomfortable for the pregnant woman, since it is during these early stages that nausea and vomiting of pregnancy manifest.

Second quarter

It is the central period, from the 13-14 to 26-28 weeks, during which the formation of all her organs is completed during the first trimester, the mother is better from the initial symptoms and still does not show the discomfort of the end of pregnancy.

The third trimester

These are the last weeks, in which the fetus has already acquired a considerable weight and volume responsible for the discomfort that pregnant women refer to by carrying that weight with them.

 the fetus matures its organs so that they can adapt to outside life, they will stop feeding and breathing through the umbilical cord to do it directly through the oral and respiratory route. It is the period from which the fetus is viable abroad, so It is advisable not to make long trips or intense physical activity.

In any case, if we make an effort to be precise in the calculations, the nine months and 40 weeks since the last period, or the 38 from the conception coincide in the same estimated date of delivery.

How pregnancy is calculated

Popularly, pregnancy is calculated in months and gynecologists calculate it in weeks and it is very common that the accounts of one and the other do not coincide. The reason, on the one hand, is those two weeks of lag, which should not be taken into account, and on the other hand that we commonly equate the months to four weeks, which is imprecise, since most months have 30 or 31 days, which are not equivalent to four weeks.

In addition, most pregnant women give birth in the three or four days before or after that estimated date, which is when the week 40. But there are also those that are advanced or delayed within the period that we consider normal for a full-term delivery.

• Before week 37 it is considered premature labor (They present the risk of the immaturity of the fetus that, although it has all its organs formed, is not prepared for life outside the womb ahead of time)
• After week 42 it is considered a postmature (they more frequently present fetal complications due to the aging of the placenta)

Both cases pose a risk to the newborn and should be avoided. The more premature, the more problems the fetus can present. There have been cases of extreme premature babies, half a kilo and 24-25 weeks, who have survived, but frequently have serious health problems. So the more weeks in the womb, the better, until the end of 37-38 weeks.

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Specialist in gynecology and obstetrics