Due dates may seem pretty straight forward, but in many cases, they are not. Most people assume that the due date is exactly 40 weeks after the first day of the mother's last menstrual period (LMP). Not so. There are a lot of things that can come into play when determining due date - I don't even understand all of them, but I do know that if a woman does not have a regular 28-day cycle, the due date can be off if determined in the method described above.
In my case, the first day of my LMP was December 2, 2012. 40 weeks from that day would put me at a due date of September 8, 2013. However, this doesn't take into consideration that my cycles were running 36 days instead of 28... pushing ovulation and conception back more than a full week. An early ultrasound estimated my due date to be September 13, which is closer... but adjusting based on 36 day cycles and when I know I ovulated puts me at a due date of September 16.
This can be important because if my care providers were considering my due date to be September 8, they might be trying to induce me or schedule a cesarean by September 16, when in reality, the baby's lungs may not yet be mature. It's important to realize that a due date is just an estimate, and can be way off.
The same situation happened when I was pregnant with Kelsey. I was running 37 day cycles at that point. 40 weeks after my LMP would have given me a due date of April 15, 2010. However, the OBs used my due date based on early ultrasound, which was April 22. Kelsey was born on April 26, which is only two days past what my due date would have been when taking my 37 day cycles into consideration (37-28 = 9, 15+9 = 24, so the most accurate due date would have been April 24).
I'm glad you are on top of knowing this - too many doctors would probably push the c-section too early in cases like this!
ReplyDeleteI have no doubt many babies are taken too early for the same reason. Very sad when a perfectly healthy baby has to spend time in the NICU because it was induced or taken via c/s before it's lungs were mature. :( I can understand it if it was medically necessary (preeclampsia, etc), but not just because. :(
DeleteSo if my cycle was 33 days, I'd do 33-28, giving me 5 days. Sept 27 plus 5 days, gives me Oct 3, right?
ReplyDeleteOkay, this is going to be long.
DeleteYup, that's right, as long as Sept 27 was based on 40 weeks after your LMP. There are other considerations, too - like when ovulation and conception occur... most women ovulate two weeks before their period, but there are exceptions to that.
I know this baby was conceived on Christmas Eve, because I was tracking some of my fertility signs indicating ovulation and charting when we had sex (iPeriod app is great for this). Going off of a due date of September 8th (40 weeks after LMP) puts conception at December 16th, but I was NOT ovulating that week. December 24th conception also gives me a September 16th due date (so adjusting based on cycle length checks out).
The method of adding the extra days to the due date is the method my midwives used to find my due date, and it matches with what I know about my body and what I've read. OBs generally either use LMP or early ultrasound - I'm glad that they do at least consider early ultrasound, because I think it saves a lot of women from being considered overdue before they really are. Early ultrasound is fairly accurate (whereas late ultrasound is not accurate at all for dating/sizing baby).
I recommend reading "Taking Charge of Your Fertility" by Toni Weschler. I have still yet to finish it (which is why I can't elaborate more than the basics), but it is an amazing book for teaching women about their bodies - you can learn how to prevent pregnancy as well as how to conceive and date your pregnancy with it. Kelsey will be reading it as a teenager, for sure.
http://www.amazon.com/Taking-Charge-Fertility-Anniversary-Edition/dp/0060881909
I'm not sure about the actual conception date, because, well, there are quite a few possibilities, lol. But my early ultrasound and LMP calculations matched, so I am thinking we're actually pretty close to the true due date. Regardless, she can stay in there until she's ready.
DeleteGood plan. :) Babies come when they are ready. I should have said in my first reply that obviously the due date is just an estimate - I came spontaneously 10 days before my due date, and my brother came 15 days after his. It does sound like you're pretty close to accurate, though, if LMP and ultrasound match. :) We'll just have to see when Kate decides to come. It can be so tough to wait at the end of pregnancy, but it is worth it in the end.
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