New Study: Due Dates are Really a Guesstimate

That due date they give you at your first prenatal visit, then maybe confirm with your first ultrasound? Very not so accurate, it turns out.

In our single birthing class they told us to think of it as a “due month,” but a new study says that it’s actually a “due five weeks.”

Only about 4 percent of women give birth on their due dates—this, we knew. But by measuring the hormone levels of urine from 125 women trying to get pregnant in the 1980s (this study was an evaluation of older research), they were able to say exactly when pregnancy began. And they found, excluding preemies, that there’s a natural variation from 38 to 43 weeks after the first day of the woman’s last menstrual period.

Interesting, but not shocking, news. But hopefully this study and perhaps others like it will start drilling home to some docs that induction can often wait. My doc, who is pretty low intervention, recommends induction at 40 weeks, highly encourages it at 41, and requires it at 42. It’s thought that the placenta may begin to degrade around this time—and also, amniotic fluid may begin to leak, compromising baby’s safety. But it all also may be absolutely fine, with baby needing that full cooking time. Her practice does lots of scans during that “extra” time to make sure everything is cool if the patient doesn’t want to induce.

Actually disturbing is that many docs encourage induction at 36, 37, or 38 weeks (in perfectly healthy pregnancies) because they believe this will mean smaller babies who are easier to deliver. But as the March of Dimes’ “39 Weeks” campaign points out, induction too early can compromise essential brain development and may lead to developmental disorders and other health problems later on. Induction drugs can also lead to a cascade of further intervention, and is one of the reasons our country has such a high C-section rate (33 percent)—induction doubles the chance that you’ll have one.

The bottom line, if your doc wants to induce because you’re “past” your “due date” (or even well before), ask questions:

–       Why do you recommend this?

–       What are the potential risks?

–       What if you’re inducing at 37 weeks for convenience and it turns out my baby needed the full 40 or more? What are the potential consequences of that?


–       Can some simple diagnostic tests (sonogram, etc.) replace or stave off your desire to induce?

Here are some great facts and more info from March of Dimes on why it’s ideal to wait, as long as there are no health threats present.