Due dates, whether calculated from the first day of the last menstrual period or from measurements taken via ultrasound, are only estimates of when delivery may occur. The most accurate way to determine your due date is from an early ultrasound any time after seven weeks gestation. Many women deliver their babies before their due date just as many women will carry their pregnancy beyond their due date. Just as there are people a little shorter or a little taller than average, there are pregnancies that are a little more or a little less than 40 weeks. A pregnancy that had gone more than 10 days beyond the due date is called ‘post-dates’.
Usually there is no obvious reason why a woman will carry her baby beyond 40 weeks. Sometimes there is a miscalculation in the estimated due date.
Usually an overdue baby is born healthy. Overdue babies do have some risks. They are more likely to gasp and take meconium (the baby’s first bowel movement) into their lungs, which can make it difficult for the baby to breathe. Also, although it is very rare, there is an increased risk that an overdue baby will be stillborn. There are also increased risks to the mother with pregnancies that go beyond 42 weeks.
Together with your health care provider, you will decide how to approach your post-date pregnancy. You may decide to wait for labour to begin naturally with or without enhanced testing to ensure the baby is still healthy. Your health care provider will likely recommend daily kick counts and may suggest non-stress tests (checking the baby’s heart rate) twice weekly, or that you have your amniotic fluid volume assessed by ultrasound. Or you may decide to have your labour induced. Current research shows that induction at 41 to 42 weeks is safer for the baby than a “watch and wait” approach, and does not result in an increased risk of Caesarean section.
You may have heard that having sex can help labour start – some studies have shown this may help, and some have shown no effect.
Your care provider may try to make your cervix more ready for labour or actually induce labour through a number of methods including: