When is my baby due?

When is my baby due?

When is my baby due?

At your first antenatal visit, your GP will calculate when your baby is due to be delivered, based on the information you provide about the first day of your last menstrual period (LMP). Your baby's estimated delivery date will subsequently be referred to at all antenatal appointments as your EDD (estimated date of delivery).

How is it calculated?

There is no great mystery attached to calculating your EDD. In fact, it is a fairly simple process. The duration of a normal pregnancy is calculated as being 280 days from the first day of the last normal regular menstrual period. Translated into months this translates into 10 lunar months, or 40 weeks.

If pregnancy were to last for nine calendar months, as is the common perception, this would roughly work out at 36 weeks. Because it actually works out at 40 weeks, it is standard practice at antenatal clinics in Ireland to discuss the duration of pregnancy in terms of weeks, and not in months.

One way of calculating your estimated date of delivery is to subtract three calendar months from the first day of your last period and then add seven days to this figure. The final figure arrived at will be 280 days from the first day of your last period.

To simplify this, let's take a couple of examples:

If the first day of your last period was February 10, (in a year that is not a leap year) the subtraction of three months would take you through January 10, December 10 and November 10. Adding seven days to November 10 would bring you up to November 17 which would be your EDD.

Another way in which you could work out your EDD, and perhaps an even simpler method, is to count forward nine calendar months from the first day of your last menstrual period and then add seven days to that figure. For example, if your last menstrual period was on December 30 and you count forward nine calendar months you would arrive at September 30. Adding seven days to September 30 would bring you to October 7 which would be your EDD.

Is my baby likely to arrive on its EDD (estimated date of delivery)?

No, is most definitely the answer to this question. In fact, fewer than 5% of all babies are born on their estimated date of delivery. However, the chances of your baby being born either sometime in the two weeks before, or after, its due date are placed at approximately 85%.

What if I am unsure of my dates?

If you have an irregular menstrual cycle, or if you experience slight bleeding early in pregnancy which may be mistaken for a menstrual period, the only way in which your estimated date of delivery can most accurately be calculated is by means of an ultrasound scan.

In Ireland, a routine ultrasound scan is often offered to expectant mothers with the first 20 weeks of pregnancy to make sure that the foetus is developing properly and that the placenta is providing sufficient nourishment.

Early scans will also be offered when there is a history of recurrent miscarriage, vaginal bleeding in early pregnancy, or in cases of a twin or multiple pregnancy.

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