Term calculation

How long does a pregnancy last?

A pregnancy lasts on average 40 weeks. When a woman becomes pregnant, her due date is calculated at the first doctor's appointment. The due date is the day when the woman has been pregnant for 40 weeks.

It is important to know that there is also a due period. It lasts from pregnancy week 37+0 to pregnancy week 42+0. Giving birth within this timeframe is called giving birth on time. Here your baby is full-term. It is only about 2% of babies that are born on the due date. It is therefore not so important for you as a pregnant woman to focus on the due date, but much rather on the due period.

How is your due date calculated?

Midwives and doctors calculate the due date based on the first day of your last menstruation. 280 days, equivalent to 40 weeks, are added to this, thus you get your due date. You can calculate your due date yourself by taking the date of the first day of your last menstruation + 7 days + 9 months. Thus you get the due date.

However, calculating the due date in this way requires that your menstruation has been regular and with a cycle of about 28 days.

If you have been in fertility treatment, you know with great certainty when you had ovulation. That date can also be used to calculate the due date. An egg can be fertilized within a relatively small window of 24-48 hours after ovulation. This allows for a reasonably certain due date calculation by taking the date of your ovulation + 266 days (equivalent to 38 weeks).

If you/you accept the offer of a 12-week scan at the hospital (which can actually be between pregnancy week 11+3 – 13+6), then the due date will be set here based on your baby's head circumference. The due date that is found at the scan is the one that will be used for the rest of the pregnancy.

What is the due date used for?

• We healthcare professionals use the due date to keep track of your pregnancy course, e.g. when the individual examinations should be scheduled
• We healthcare professionals also use the due date to assess your/your baby's growth
• The due date helps determine the recommendations for you/you
• The due date is used to determine the date for when you can go on maternity leave
• The due date helps determine when an induction will be recommended

The due date itself is therefore primarily a working tool for professionals and the labor market. For those of you expecting a child, the due period is what I would recommend you focus on.

With wishes for a good pregnancy

Warmly

Siff Stephenson, HjerteJordemoderen