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Length of human pregnancies can vary naturally by as much as five weeks

7 August 2013

The length of a human pregnancy can vary naturally by as much as five weeks, according to research published online in Europe’s leading reproductive medicine journal Human Reproduction.

Normally, women are given a date for the likely delivery of their baby that is calculated as 280 days after the onset of their last menstrual period. Yet only four percent of women deliver at 280 days and only 70% deliver within 10 days of their estimated due date, even when the date is calculated with the help of ultrasound.

Now, for the first time, researchers in the USA have been able to pinpoint the precise point at which a woman ovulates and a fertilised embryo implants in the womb during a naturally conceived pregnancy, and follow the pregnancy through to delivery. Using this information, they have been able to calculate the length of 125 pregnancies.

Read the press release.
Read the full paper.