When am I due? The truth about due dates.



First, congratulations, and we hope you enjoy this amazing journey. However, an online calculator isn’t the very best way to figure out your estimated due date. Updated guidelines for estimated due dates came out this month from the American College of Obstetricians and Gynecologists: They say counting out 280 days (40 weeks) from the first day of your last period isn’t accurate enough to allow for optimal prenatal care. That calculation is based on the assumption that every woman has a 28-day cycle and ovulates on day 14. The truth is that around 80 percent of women deliver anywhere between 37 and 42 weeks.

The new guidelines recommend an ultrasound during your first trimester so the fetus’s precise size and head circumference can be measured. That, taken with the info about your last period, allows a far more accurate estimated due date. For example: If you have an ultrasound before you’re 14 weeks along and the fetal size suggests a due date that’s more than seven days different from an estimated due date based only on your menstrual period, the ultrasound due date should be the one that is accepted as accurate. If your pregnancy was from in-vitro fertilization, the latest guidelines state that your estimated due date should be calculated from both the age of the embryo and the date of the transfer.

Whatever your due date is, remember: get regular prenatal check-ups; take prenatal vitamins; eat a baby-healthy diet (you’re eating for 1.1 not two people); and don’t gain too much weight (25-35 pounds if you started at a healthy weight, 15-25 pounds if you’re overweight, less than 15 pounds if you’re obese). And pick up a copy of our book “You: Having a Baby.” It’ll help you consider and plan for the many choices you’ll be making — from food to delivery location. Good luck with your labor of love!