Nine months or at least ten months **Duration? pregnancy** When first heard, it is often the first question that raises the question of when the baby is born. There are different calculation methods for the possible delivery date. Most are based on the last menstrual period as a basis. Read more about the different methods of pregnancy calculation and their duration.

## Pregnancy: Calculation after menstruation

Most women do not know the exact date of conception, but the first day of the last menstrual period. On this basis, the duration of pregnancy can be calculated using the so-called Naegele rule: in a regular cycle of 28 days, seven days and one year are counted from the first day of the last menstrual period and then subtracted three months. The result is considered a possible delivery date. Example:

Last period on 30.05.2015 + 7 days + 1 year = 06.06.2016 - 3 months = 06.03.2016

According to the Naegele-rule, a pregnancy lasts mathematically 280 days (40 weeks).

But how long does a pregnancy take if the cycle is irregular? In such a case, the days deviating from the 28-day cycle are added or subtracted from this calculation. This so-called extended naegele rule is most commonly used in pregnancy to calculate the duration.

## Pregnancy: Calculation after the time of conception

If, on the other hand, you know the time when the concept was generated, the calculation is simpler: seven days and three months are deducted from the conception date and one year added. This results in a calculated pregnancy duration of 267 days.

## If neither conception nor last menstrual period are known

In rare cases, the cycle information is extremely inaccurate. If the time of conception is also unknown, none of the abovementioned calculation methods can be used. The first appearance of child movements is then taken as an indication: first-time mothers notice the first movements around the 20th week of gestation, second or multiparous women around the 18th week of pregnancy. With deviations of two weeks sooner or later, these child movements thus give indications of the duration. In such cases, however, pregnancy also means that one has to live with greater inaccuracies.

## Calculation with ultrasound

A very accurate determination of the age of the child is possible today with an ultrasound examination. Because in the first few weeks, the size of the embryo is closely related to the gestational age. The diameter of the amniotic sac can be measured from the seventh week, and the first heart sounds of the embryo are already audible six weeks after menstruation.