Pregnancy by Weeks: The First Question You Get Asked

Armen Hareyan's picture
Pregnancy, ultimate week by week guide
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Earlier this year, Wiley published the second fully updated and revised edition of Dr. Laura Riley's "ultimate week-by-week pregnancy guide called You & Your Baby. The following is a little excerpt from the book where Dr. Riley discusses the first question pregnant mothers are asked and how the due date is calculated.

Calculate Your Due Date

When is your baby due? That’s one of the first questions you’ll get asked after you announce your pregnancy. To determine that date, your health care provider will start by asking you the first day of your last normal menstrual period (LNMP). She will add 266 days, or thirty-eight weeks, to that date. (Why thirty-eight weeks? It’s the length of the average pregnancy from the point of conception.) She will then tack on yet another fourteen days because that’s the average number of days between the start of your last normal menstrual period and ovulation.

Calculate your due date. You can estimate your own due date in a simpler way: Figure out the first day of your last normal menstrual period and add exactly nine months and seven days to that date. For example, if the first day of your last menstrual period was January 3, you would add nine months and seven days to that date. Your due date would be October 10. Better yet, go online and type in “due date calculator.” Several sources will appear at your fingertips.

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Important Steps After You Learn First Signs of Pregnancy

No matter what you think your due date is, hold off on printing your baby announcements until after the baby arrives. Babies have a will of their own, and your due date is not completely predictable. In fact, the actual medical term for a pregnancy due date is an “estimated date of delivery,” or EDD.

Why the emphasis on estimated? You may be unsure of the date of your last menstrual period, for instance, or you may have irregular periods. It’s also possible that you don’t ovulate in the middle of your cycle but much sooner or later than that magical, “average” fourteenth day.

In fact, even if you do have periods that run like clockwork and you know exactly when you had intercourse, calculating your due date is still an inexact science. Sperm can take three days to travel through your fallopian tube to meet up with your egg, so the date of conception isn’t always the same day you had intercourse. Your health care provider will probably caution you that your due date is only an approximation. After all, only about 5 percent of all babies are born on
their predicted due dates!

Excerpt from You & Your Baby: Pregnancy
Dr. Laura Riley, OB/GYN
Copyright 2012 John Wiley & Sons, Inc. All rights reserved.
ISBN 978-1-118-08411-3 (pbk)

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