Searching for a Due Date Calculator? There’s an App For That

Due date calculator

Actually, turns out there are a bunch of apps for that, but only one that has the imprimatur of the American College of Obstetrics and Gynecology (ACOG).

When I was pregnant with my daughters, who are now teenagers, I remember playing with the old-fashioned pregnancy wheel, the plastic thingy that was really a double wheel. You’d turn the inner wheel until the line labeled “first day of last period” aligned with the proper date on the outer wheel, which traditionally is 280 days after the first day of your last menstrual period. Got that?

Not surprisingly, the new estimating due date calculator added in January to ACOG’s primary app is somewhat more sophisticated than the plastic pregnancy wheel, which, at least as far as ob-gyns are concerned, is supposed to go the way of men sitting in a waiting room while their wives labor behind closed doors.

“Unlike other calculators, the Estimating Due Date Calculator that is contained in this ACOG app is based specifically on guidance from The American College of Obstetricians and Gynecologists, the American Institute for Ultrasound in Medicine, and the Society of Maternal-Fetal Medicine,” according to the introduction to the app.

Here’s what’s different about the ACOG calculator compared to the other due date calculator apps: It uses not only the first day of your last menstrual period but also an ultrasound exam to determine the gestational age of the fetus and the estimated due date.

Why is that important? “Ultrasound measurement of the embryo or fetus in the first trimester…is the most accurate method to establish or confirm gestational age,” according to an opinion statement issued in October 2014 by ACOG, the ultrasound group and the maternal-fetal medicine society.

Estimating your due date based only on when your last period began is problematic for a few reasons, the opinion notes. That method assumes that your menstrual cycle is without exception 28 days long, with ovulation occurring 14 days after it begins. The problem is that not all menstrual cycles are created equal. While yours might be 28 days, your friend’s might be 26 or 30. Plus, not all women necessarily ovulate exactly 14 days after their period starts, no matter how long it is. To complicate matters even more, unless you routinely record the dates of your periods, chances are you might not remember exactly when the last one started.

And an accurate estimate of your due date is important to your health and that of your baby.

Falling short by a few days might not seem like a big deal. But it could mean the difference between a baby born full term and one born preterm, due to inducing labor or scheduling an elective c-section too early. Babies born even a few days preterm, or before 37 weeks’ gestation, are at a higher risk of medical complications than babies born fullterm.

If your estimated due date is a few days off in the other direction, and your baby could be born post term. A post term pregnancy is one that lasts 42 weeks or longer, and it is associated with an extra-large baby, which increases the risk of needing a c-section.

While ACOG’s estimated due date calculator is primarily designed for physicians, the organization notes that it’s straight-forward enough for all members of the health-care team, including patients. You can download it for free from the Apple App Store or Google Play for Android (remember, it’s part of ACOG’s updated primary app, not a separate app, so don’t do what I did and start searching for a specific ACOG due date calculator).

As for any of those plastic pregnancy wheels you might have lying around, I hear they make great coasters.

Rita Rubin
An ob-gyn's daughter and the mother of two teenage daughters, Rita Rubin has covered medicine ever since earning a BSJ from Northwestern. Based in Washington, D.C., Rita has written for WebMD, JAMA, POZ, and NBCNews.com and previously worked for USA TODAY. She has won numerous awards for her stories and authored What If I Have a C-Section? Rita earned an MA in writing from Johns Hopkins and spent a year as a fellow at the Harvard School of Public Health. You can follow her on Twitter @RitaRubin.

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