Length of pregnancy can vary by up to five weeks, scientists discover

The length of a pregnancy naturally varies between different women by as much as five weeks, scientists have discovered for the first time.

Although it has always been known that human pregnancies usually last between 37 and 42 weeks, the variation has previously been attributed to imperfect methods of estimating due dates.

A woman’s due date is calculated as 280 days after the onset of her last menstruation and is only ever considered a best guess. Only four per cent of women deliver on their due date and only 70 per cent within 10 days of it.

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