Calculating the due date
How far overdue before induction?
Is my cervix ripe?
Tests for an overdue pregnancy
What overdue babies look like
When is my baby due?
The date a baby is due to be born, is often referred to as the estimated date for confinement (or 'EDC') or the estimated date for delivery (or 'EDD'). In truth, it is precisely that, an estimate! We really don't know how long it takes each individual woman to grow a baby. The normal length of any pregnancy is regarded as the baby being born any time from about 37 to 42 weeks.
The universal use of a '40 week' gestation was first developed by a German obstetrician called Naegele in the 1800's. He declared that a pregnancy should last 10 lunar months or 40 weeks, which is 280 days, or about 9 calendar months (although we now know that a lunar month is 29.53 solar days, meaning 295 days, which is closer to 42 weeks!)
A study done more recently (in 1990) found that the average length of a pregnancy was about 40 weeks + 8 days for first time mothers, and 40 weeks + 3 days for mothers having their second, or subsequent babies. The high percentage of
inductions in Australia contributes to the average length of pregnancies being a little under 39 weeks.
If women were left to go into labour spontaneously (or on her own):
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About 50% of women would have their baby between 39 and 41 weeks. |
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Only about 5% of babies would be born on their actual due date. |
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Up to 88% of women would have their baby between 38 and 42 weeks. |
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About 6-7% of babies would be born premature (before 37 weeks). |
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If not induced, a small number of babies would be born after 42 weeks. In 2003 in Australia, about 1.5% of babies were born in the 42nd week or more. |