Counting the Weeks and Months of Pregnancy
by Nancy Sullivan, CNM, MS, FACNM

Q. I was wondering if you could give me a break down of how the weeks of pregnancy equal in months. I seem to get conflicting answers.

A. We seem to have made this as confusing as possible; don't ask me why! The average pregnancy has 280 days, 40 weeks, or 9 months plus 1 week, counted from the first day of the last menstrual period. In other words, we start counting about two weeks before the baby is actually conceived. We also talk about "trimesters" of pregnancy; the first trimester is weeks 1-12, the second weeks 13-28, and the third weeks 29-40 or whenever the baby is born. To make matters even more confusing, recent statistics have shown that the average pregnancy these days is actually closer to 41 weeks; in other words, your baby is likely to come about a week later than that "due date" you are so focused on. I like to talk about a "due month" with my patients; that is really much more realistic.