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Accurate due date calculator5/24/2023 The rule is more unwieldy, but studies suggest it’s at least twice as accurate as Naegele’s rule.ĭepends on which gestational age you’re talking about. The Mittendorf-Williams predicts that the average pregnancy lasts 288 after the last menstrual period for Caucasian first-time mothers, and 283 days for Caucasian non-first-time moms. Nearly two centuries after Naegael took obstetrics by storm, physicians Robert Mittendorf and Michelle Williams developed a computer model for estimating due dates that considered 16 factors, including maternal age, race, weight, coffee intake, and pregnancy history. Or, put another way, you can set a reasonably reliable baby deadline by calculating 294 days from your last period.Īlternatives: The Mittendorf-Williams Rule This will give you a “due month”, and 80 percent of babies will arrive within that window. For a more accurate guess, add two months to the due date in either direction. Only about 4 percent of babies are born on their due dates as determined by Naegele’s Rule. With a little elbow grease, you can make Naegele’s ballpark estimate even more accurate by adding one day to the due date for every day your cycle is longer than 28 days, and subtracting one day from the due day for every day that it’s shorter. The average menstrual cycle is 28 days long, with ovulation occurring at day 14. He predicted childbirth exactly 280 days after the last menstrual period before getting pregnant. Franz Naegele, a German obstetrician, came up with his eponymous rule in the early 1800’s. Online due date calculators generally rely on the simple, if somewhat inaccurate, Naegele’s Rule. Here’s how to calculate your due date like a scientist: ![]() The better you understand the margin, the better you understand what to expect (and how to create a birth plan). The next step? Getting an ultrasound that misassigns a “gestational age.” The question expecting couples find themselves struggling with is this: What does any of it mean? Essentially, it means that there is a flawed way of calculating a birth date to within a margin of error. For many people, ball-parking infant ETAs involves entering menstrual, height and weight, and coffee drinking data into a due date calculator in service of getting a number that is all but guaranteed to be wrong. Pregnancy due dates are notoriously unreliable. Babies are born after nine months-sort of.
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