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• C SECTION DUE DATE CALCULATOR FULL

She noted that in 2006 the most common week to deliver in was the 39th about 30% of births occurred then.

data for singleton births, from the Centers for Disease Control, to try to answer this question. In her book Expecting Better, Emily Oster used the 2006 annual U.S. So when are pregnant women actually most likely to deliver? When evaluated by ultrasound dates alone, they found the majority, 71.5% percent, of these pregnancies were not actually post-term. The researchers studied inductions for post-term (past 42 week) pregnancies. Who really cares? Actually, this bias matters a lot. An estimate off by even a couple of days significantly raises the percentage of women regarded as post-term (past 42 weeks), who are then urged to have inductions.Ĭonsider the results of a UK study of over 24,000 women. Using ultrasound-based due dates, 92% of pregnancies delivered within the normal range of 37-42 weeks using due dates, this percentage fell to 87%. Adding 282 days to the first day of the last menstrual period, instead of 280, provides a more accurate estimate. But, if available, an estimate based on a first trimester ultrasound is the best option. Is there a more accurate way to calculate a “due date”?

C SECTION DUE DATE CALCULATOR FULL

For unknown reasons, women of Asian or African ancestry tend to give birth about a full week earlier than do Caucasians. Note, though, that estimates apply best to Caucasian women. Other large studies back up these findings: Naegele’s rule consistently underestimates the average delivery date by 2-4 days (see here). Another study of 1,514 women with reliable conceptions dates found that first-time mothers went an average of 4 days “late ” women with a previous birth went 2 days “late.” In a study of 114 Caucasian women, women with 1 or more deliveries under their belts delivered an average of 3 days after their due dates first time mothers delivered an average of 8 days after their due dates. The second problem, bias, is far more concerning: The average actual delivery date is later than the one predicted by Naegele’s rule. This is especially true for first-time mothers. Have a shorter cycle, and the due date may overestimate it. Have a longer cycle, and the due date will likely underestimate the real delivery date. And many, many women’s cycles are shorter or longer than 28 days. The first, imprecision, is pretty obvious to people with ovaries: His rule assumes menstrual cycles are consistent in length, exactly 28 days long, with ovulation occurring precisely on day 14. Not surprisingly, Naegele’s rule has some problems. His calculation of pregnancy length relied not only on the duration of actual, observable pregnancies, but was also greatly influenced by biblical scholarship indicating that the gestation of Christ lasted for ten lunar months. Naegele, a director at a German hospital, developed his rule in the early 1800s, long before ovulation predictor kits, over-the-counter pregnancy tests, prenatal ultrasounds, fetal nonstress tests, pitocin–in short, before all of modern obstetrics. Naegele’s rule has proved remarkably enduring.

The “due date” comes from a calculation known as Naegele’s rule, in which 280 days are added to the first day of a woman’s last menstrual period. If you have severe gestational diabetes, and your due date will likely be treated as a hard stop, and your doctor will insist on an induction at the 40 week mark. Go two weeks past and an induction is all but assured. Go a week past yours, and you will be urged to have labor induced. So why care about the due date at all? Well, modern medicine has given us one very concrete reason for concern: Due dates act as a medical deadline. No, the average, the mode, and the median delivery days are all 1-4 days after the “due date“.

It is NOT the day by which half of pregnant women have typically delivered, and half have not (the median). The due date is NOT the average delivery day of a large, modern reference sample of pregnant women. The due date is also NOT the day on which pregnant women most commonly deliver (the mode). If you knew nothing about due dates, you might reasonably suppose that the due date is the average date of delivery.Īnd you’d be wrong. And yes, most women will deliver within 2 weeks of their so called “due date”.Īctual birth data, from real pregnant women, shows that the due date is not only an imprecise delivery estimate–as any single day would be–it is 1-4 days too early. Yes, the due date is not a precise date, only an estimate. Can we please stop with this due date nonsense already?