Why is pregnancy counted by weeks and not by months

When a woman becomes pregnant, her life begins to register for weeks. Almost without knowing why, from the moment the positive appears in the pregnancy test, we instinctively think about the weeks that the future baby has.

Everyone knows that a pregnancy lasts 40 weeks, or what is the same, 9 months, right? Well, I invite you to do some simple accounts, it is easy not to stop to think about it or not to give it importance, really what matters to future parents is that their baby is perfectly healthy.

Have you already counted? If so, you will have verified that 40 weeks is equivalent to a period of almost 10 months. Then Why is a pregnancy said to last 9 months? This has a somewhat convoluted explanation, but I will try to explain it to you in the simplest way.

Why are 40 weeks of pregnancy?

The gestation period begins during ovulation, but curiously when you have the first appointment with your doctor, the question he asks you is when was the first day of your last period.

What can lead to think that the pregnancy begins at that moment. Actually, this is because, it is very common for women to have control of our menstruation, and not our ovulation period.

So, taking into account that on average the menstrual cycle occurs every 14 days, and ovulation occurs about 6 days before the next period, we can calculate that at that time we have XNUMX weeks of pregnancy.

Which is actually when the last ovulation occurred. Therefore, we could say that a pregnancy lasts 38 weeks but added those 14 days of estimation, the forty weeks appear.

This is the reason why a pregnancy of between 37 and 42 weeks is considered full term. That is, from that moment the baby can be born at any time with less risk, because it is already fully formed.

However, these accounts are effective at the beginning of the gestational period. But, until a first ultrasound is performed, we will not be able to know the exact time that the fetus has. That is why perhaps in the first visit, the midwife will give you a probable due date and when the first ultrasound arrives, that date will be earlier or later.

Through ultrasound, the weeks of gestation can be more accurately detected. It is possible that one day we dance when it comes to calculating the last rule. Even, ovulation does not always occur exactly 14 days after the first day of menstruation. There may be a variation of between 7 and 21 days.

That is why in the first trimester ultrasound, the probable date of delivery will almost certainly change. As a variation of a single day can induce labor unnecessary.

How the trimesters of pregnancy are divided

Therefore, since we know why pregnancy is counted in weeks, let us also know why is it divided into quarters.

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In each of these periods, physiological changes occur. This for the purposes of its control, it is more efficient to value in quarters.

In the first trimester, the organs and tissues of the embryo begin to develop. Your fingernails and toenails are also beginning to form. This occurs from week 1 to 12 weeks of pregnancy.

The second quarter It ranges from week 13 of gestation to week 26. In this period, the embryo is called a fetus. At this stage it is already possible to determine the sex of the baby. The organs continue to develop and the baby is placed in the fetal position.

The third and last trimester, begins at week 27 and ends at delivery. During this period the organs will finish forming and the baby will be ready to survive outside the womb.

By separating the weeks of pregnancy by quarters, it is easier for specialists to determine if the development is occurring correctly.

In short, both counting the pregnancy by weeks, and dividing it into trimesters, has simple practical reasons for medical purposes.