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  • Dr. Katie O'Connor

Overbaked or Underbaked? How do you know when your baby is due?



We’ve all known her. That pregnant mama who’s feeling large, sweaty and can’t get comfortable. She’s past her due date, and she’s already posted out on social media asking her friends for their top tips in getting labor started. She paints the perfect picture for us of what it’s like to be “past due” in pregnancy.


The interesting thing is in my years working with pregnancy mamas, I’ve known this mama quite a few times. However, I’ve also known this same mama, feeling the same way, only she’s only 37 weeks. I’ve known mamas at 41 weeks who, while still large and in charge, overall feel really great. The fact is that being “overdue” when pregnant isn’t really the thing it’s made out to be.


Have a baby is not like borrowing a library book or having a car payment. Those things are certainly due when their due, and there’s a penalty for not returning or paying by that due date. Giving a newly pregnant mom a “due date” often puts that same limiting feel on something that is fluid, individual, an estimate and frankly not very well understood even in the literature.


I’ll say it again. A due date is an estimate. Yet unfortunately for mom and baby it’s often not treated that way and can lead to stress, disappointment, fear and frequently, unplanned interventions.



Now I’m not saying that we should get rid of due dates all together, because there are some positives. Knowing roughly when you can expect your baby to arrive is certainly important, and it does give you that finish line to look forward to, especially when you’re not feeling so hot. What I am saying it that we might treat it more like an ETA (estimated time of arrival). Explain to the mother when you’re giving her the estimated due date that it is in fact an estimate and that her baby could arrive either before or after and still be perfectly healthy.


Because that’s the truth.


Here in the states, many women are made to feel like anything outside their due date is nearly pathological, especially going after their date. In addition to that, doctors often time interventions such as cervical ripening, membrane stripping or even induction based off of this magical date despite the fact that many of these interventions aren’t showing improved birth outcomes in the literature.


So let’s talk about how a baby’s due date is calculated. The general rule of thumb is to take the date of moms last menstrual period and then add 280 days to that date. Here’s where you can see that this is an estimate. First, there’s the expectation that every gestation period (the time it takes to grow a baby) is the same 280 days for every woman. It isn’t though. In a study done where researchers tracked women’s actual date of ovulation (meaning the knew the actual date of conception) there was a five WEEK variance among all the women’s length of pregnancy!! The other issues with this are that many women have irregular cycles, didn’t track the exact date of their last period or ovulate on a completely different cycle day than the general estimated “day 14”.



This lack of regularity has now led practitioners to often do a 6-8 week ultrasound, which is somewhat more accurate as they are measuring fetal size. Statistics still show that even using this method only 5% of babies are actually born on their due date with a variance of 11 days on either side of the pregnancy. You also have to take into account that even those statistics will be skewed by the fact that "late" pregnancies are rarely allowed to continue on to natural labor which would tend to increase the range further if these women went into labor on their own.




So what is my point in all of this?


My first point is that physicians should give their patients a more informed version of their estimated baby arrival so that parents can expect a range of possibilities.


My second point is that people are extremely individual. If women were allowed to believe that a healthy pregnancy could be anywhere from 37-43 weeks, there would be less stress, less intervention and fewer unmet expectations. Mothers would be empowered to know that their body and their baby would know when the time was right for baby’s arrival. Considering we still aren’t even exactly sure what causes labor to begin, it is silly to think that we know when someone should be induced unless there is a real medical emergency. Sizing ultrasounds in the third trimester have an error margin of +/- an entire pound, yet they are used to scare moms into thinking that their 41 week baby is “too big”.


Let’s get back to relaxing during pregnancy and practicing “wait and see”. Let’s let our bodies and bellies do the talking and start finding our female intuition. Let’s tell our fresh new babies that we trust them to know when it’s time and start helping them foster independence and confidence straight from the womb.








Dr. Katie O'Connor is a Webster Certified prenatal chiropractor. In practice for over 10 years, she is passionate about all things pregnancy and helping women have the best experience possible while becoming a mother.



Life.Naturally Chiropractic

16335 S. Harlem Ave

Tinley Park IL 60477

517.282.6242




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