Your due date

Research suggests that the placenta starts to function a little less well after 41 weeks of pregnancy and that this decline accelerates after 42 weeks. This is why many hospitals offer to induce women when they are between 41 and 42 weeks gestation. It is important for you and your professional carers to be sure of when your baby is due before making a decision about induction.

When you go for your initial visit to tell your doctor you are pregnant, he will ask you when was the first day of your last period before becoming pregnant. Then he will tell you your estimated date of delivery, calculated by adding nine months and one week to this date. Remember that this is only an estimated date; there are a number of other factors to consider:

• Is your menstrual cycle regular and is it a 28 day cycle? The date your baby is due is calculated as if you had a regular monthly cycle. If your cycle is shorter than 28 days, your due date should be brought forwards and if it is longer, it should be moved backwards

• If you have had an ultrasound scan to estimate when your baby is due, did you have the scan during the first 13 weeks of your pregnancy? Early pregnancy scanning is very accurate in estimating due dates, but scans carried out after 13 weeks are only accurate to within about 2 weeks (i.e. not very accurate at all)

• Do you know the exact date when your baby was conceived? If you are absolutely sure, the date your baby is due should be calculated accordingly. Under these circumstances, there is no medical evidence that can be more reliable than yours!