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31. Prolonged pregnancy

By Dr Joe Kabyemela, MD

The concept of prolonged pregnancy means different things to different people. It is an indisputable fact that most pregnancies labeled as such are not prolonged. Not that blame for this can be apportioned to anybody in particular. It is just a consequence of the doctors' attempts at meticulous management of pregnancy.

To practically every pregnant woman, if the pregnancy continues beyond the calculated expected date of delivery (EDD), it is prolonged. Pure and simple.

The expected date of delivery or EDD is calculated from the date of the onset of the last period and falls on the fortieth week from that point. This concept presupposes that a human pregnancy is supposed to last forty weeks exactly. This is, of course, not the case. In fact, those who have conducted surveys to see what proportion of women actually deliver on their calculated EDD will tell you it is less than 1%. This means 99 out of 100 women will deliver either before or after their calculated EDD. Most will deliver before. The formula also assumes that all women have a 28-day cycle, which is clearly not the case. For a woman with a shorter cycle, the gestational age will be underestimated and for those with long cycles, the reverse is true. All this is clarified further in this chapter.

It is now an accepted fact that term pregnancy is not a fixed point. In fact, there is world consensus that ‘Term’ (i.e. mature pregnancy) spans a total of five weeks. Over 80 per cent of all women will deliver, spontaneously or otherwise, during that phase. If no intervention is made, anything between 3 and 10 per cent of all women will go beyond the 42 weeks mark. In this era of meticulous antenatal care, this happens rarely. This is because most women go for induction of labour either just before or at the 42 weeks mark.

So, while most women regard anything beyond the forty weeks mark to represent prolonged pregnancy; in truth, this does not begin until two weeks later. For descriptive purposes, the period beyond the 40 weeks mark (EDD) is known as ‘post-dates’ and if it goes beyond 42 weeks, then it becomes ‘post­-term’.

The EDD is also known as the EDC which stands for ‘Expected Date of Confinement’.

Post-maturity means the same as post-term.

So, are there any potential problems associated with prolonged pregnancy? This and other related questions are answered in this section.

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Expected date Term After 42 weeks Predisposing factors Fetal wellbeing Labour in postmaturity