Calculation of the due date

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The first sign of pregnancy is usually the absence of menstruation. However, that alone is not a sufficient indication of pregnancy. However, if you experience breast tenderness at the same time and you may experience nausea in the morning, it is very likely that you are actually expecting a child.

How do a doctor or midwife calculate the time of birth?

Nobody will be able to predict the exact due date of your offspring. However, the doctor or midwife is able to narrow down the time of the birth. The duration of a pregnancy counts from the first day of the last menstruation - even if the time of conception does not occur until about 14 days later with ovulation. According to this pattern, on the day you became pregnant, you are arithmetically already in the third week of pregnancy. It takes about 40 weeks in total for your baby to see the light of day.

To find out the time of delivery, proceed as follows (calculation according to Naegele's rule):

• Take the first day of your last menstruation and add a week to it. For example, if the first day of the last rule is April 1st, then adding a week results in April 8th.
• Now subtract three months, add a year and you have the due date (the date of the expected birth). In our example it would be January 8th of the next year.

The calculation is only correct if you have had regular menstrual periods approximately four weeks apart.

However, there are factors that influence the time of delivery. For example, women who stop taking birth control pills and become pregnant within the next two months often have irregular ovulation. Others, however, have no or irregular menstruation after stopping the pill. If you do not menstruate after the last pill bleeding but still became pregnant, you should add a week or two to the calculated date, sometimes more.

In the practice of your gynecologist there are so-called pregnancy calendars (Gravidarians) that can be used to calculate the due date. There are also various apps and other media that can show the likely due date.

Can the doctor decide whether the calculated appointment is correct?

An ultrasound examination carried out by your doctor in the 9th to 12th week of pregnancy provides relative certainty about the time of birth. Based on the size of the embryo and the development data, he will be able to determine the time of delivery very precisely.

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