How are pregnancy weeks considered?

Many women, only after learning about the onset of pregnancy, are wondering about what week it is considered and how. It should be noted that over the long years 2 main methods have been formed, which allow calculating the period: by the date of the first day of the last menstruation and from the moment of conception. The duration of pregnancy obtained as a result of calculations using the first method is called the obstetric term.

How do doctors determine the duration of pregnancy?

Before gynecologists calculate the number of weeks of pregnancy, they will learn about the date of the first day of the month. It is the starting point for setting the deadline in this way.

As you know, a normal pregnancy lasts 40 weeks. Thus, in order to calculate the term of the expected delivery, the first day of menstruation should be added 280 days (those same 40 weeks).

This method is not very informative, because It makes it possible to establish only the estimated date of birth, which may occur earlier than the established period. This is explained by the fact that pregnancy is possible only after ovulation, which usually occurs on the 14th day of the menstrual cycle. That is why, the difference between obstetric and real term is 2 weeks.

Which method allows you to accurately determine the duration of pregnancy?

Due to the fact that pregnancy occurs after the last day of menstruation, the exact date of birth can not be established. It is much more accurate to do this by calculating the gestational age, which is considered directly from the day of fertilization. Its use is hampered by the fact that many girls, because of regular sexual relations, can not say exactly when the conception occurred.

Thus, knowing how the obstetrical weeks of pregnancy are considered , the woman will know that the period, obtained as a result of such calculation, differs from the real one by about 14 days.