Pregnancy duration can vary by up to five weeks: study

In a unique study, US researchers conducted hormone assays in daily urine samples in a cohort of women, enabling them to pinpoint the day of ovulation and the day of embryo implantation.

Among 125 women, excluding those with medical conditions and preterm birth, they found gestation ranged from 247 to 284 days.

They also found duration of previous pregnancies was a good guide to an individual’s ‘natural’ pregnancy length, and that embryos which took longer to implant also had a longer gestation period.