Pregnancy length in humans can vary naturally by as much as 5 weeks
A new study has found that the length of a human pregnancy can vary naturally by as much as five weeks.
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 percent deliver within 10 days of their estimated due date, even when the date is calculated with the help of ultrasound.