- Joined
- Apr 13, 2011
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- 393
We found that the average time from ovulation to birth was 268 days -- 38 weeks and two days," said Dr Anne Marie Jukic, a postdoctoral fellow in the Epidemiology Branch at the National Institute of Environmental Health Sciences (Durham, USA), part of the National Institutes for Health. "However, even after we had excluded six pre-term births, we found that the length of the pregnancies varied by as much as 37 days.
The 40 week number is calculated from the first day of last period, and ovulation is typically at about 2 weeks. I know, weird, but that's how we calculate it. Thus, the average being 40 weeks, though technically, for the first 2 weeks, the person isn't actually pregnant. In other words, at conception we call that 2 weeks pregnant.