Are you overdue?
Only about five per cent of all babies arrive on the actual date that they're expected. The expected date of delivery (EDD) is only a statistical average, and studies have shown that as many as 40 per cent of babies are born more than a week after their EDD. Of the 40 per cent of babies who are “overdue”, 25 per cent of babies are born in the 42nd week.
Being overdue
© DK
The exact date of conception in any particular pregnancy is extremely difficult to pinpoint, which makes it difficult to decide whether a baby is actually overdue or not. Even if you have a regular menstrual cycle of 28 days (the standard on which the EDD chart is based), the date of ovulation is known only approximately.
As well as this uncertainty about the exact date of ovulation, every baby is different and so it's unrealistic to expect them all to mature in precisely the same number of days. Since labour is initiated by your baby producing certain hormones as he reaches full maturity, it makes sense that the actual date of delivery can vary fairly widely - even in “textbook” pregnancies. Early ultrasound scans are helpful in confirming, or sometimes even changing, your due date. The earlier the scan is performed the more accurate it is.
Doctors do become worried, though, if a pregnancy continues much beyond two weeks after the estimated date of delivery. This is because post-maturity and possible problems with the placenta (placental insufficiency) pose some risks to the health of your unborn baby (see Post-maturity, Risks,). The longer your baby goes on growing inside your womb, the larger he is likely to become, which, in turn, will increase the chances of a difficult labour. There's also the risk that the placenta will not be able to continue to support your baby over an extended period (see Your baby's placenta).
Doctors will also ask you about your family history - have you or your mother had longer than average pregnancies (lasting 43 or 44 weeks for example)? If this is the case, your doctor will probably be more willing to let you go more than two weeks overdue without suggesting that you're induced - although you'll be closely monitored in case any problems do develop. In practice, most women are quite desperate to have their babies by this stage of pregnancy.
Post-maturity
An overdue baby may be in danger of being post-mature. A post-mature baby will have lost fat from all over his body, particularly from his tummy. His skin will look red and wrinkled as if it doesn't fit him, and it may have begun to peel. Very few babies are actually post-mature because post-maturity depends not only on the baby's condition, but also on his placenta. It is difficult to predict which babies will be at risk.
Risks
A post-mature baby tends to be bigger than average which can make your labour longer and more difficult. Also the bones in his skull tend to be harder, which means that his descent through the birth canal is likely to be more traumatic both for him and for you. In addition, there's an increased risk of stillbirth: the risk of stillbirth doubles by the 43rd week of pregnancy and triples by the 44th week.
Your baby's placenta
At term, the placenta - the organ that links the blood supplies of the mother and baby - looks rather like a piece of raw liver. It is about the size of a dinner plate, and measures about 2.5cm (1in) thick. The maternal side is divided into wedge-shaped chunks called cotyledons.
The placenta has substantial reserves, readily adjusts to injury, repairs damages due to ischaemia (lack of oxygen), and does not undergo ageing. The widely held view that the placenta ages progressively during your pregnancy is due to a misinterpretation of the appearance of different parts of the placenta over the duration of the pregnancy.
There are, though, changes in the character of the villi (small projections) around the placenta during the pregnancy, and by 36 weeks there may be deposits of calcium within the walls of the small blood vessels, and a protein deposit may appear on the surface of many of the villi. Both of these changes can limit the flow of nutrients and waste across the placenta to your baby, but this is balanced by the fact that the fetal blood vessels and villi are close together, which makes the exchange of nutrients easier.
Posted 16.11.2010
Get more on this subject…
