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This is a transcription of a portion of a Healthful Woman podcast.

Leah’s Question

Our first question is from Leah, “Hi, Dr. Fox. Love the podcast,” thanks, Leah, “Have enjoyed listening throughout my pregnancy. I’m a few weeks away from delivering, and my baby has been breech for a long time. So, I have a C-section scheduled. The baby has been in the same exact position every time I get an ultrasound, which has been once a week for a while due to some high-risk factors. It has me wondering what typically causes a baby to stay breech until the end. I know uterus shape can be a factor, but no one has mentioned that being the cause in my situation. Thank you.”

Dr. Fox’s Response

So, Leah, you are correct that we don’t really know for most babies why they stay breech until the end of the pregnancy when they do. The likelihood of a baby being breech at the time of delivery, meaning head up and butt down, is actually pretty low. It’s under 5%. Earlier than that in pregnancy, along the third trimester, a lot of people have ultrasounds or exams that say, “Hey, your baby’s breech. Hey, your baby’s breech,” you know, much, much higher percentage than that, like up to 50%. But almost all those babies find their way to head down by the end of pregnancy. Now, how do they do that?

So, we’re not 100% sure. We think there might be some sort of brain stimulus for them to do that, to sort of find their way head down. Others think it’s just more a function of geometry, that since the bottom of the uterus is sort of shaped like a funnel, when the feet are there, they just sort of kick around, and they don’t really wedge in there. But once the head gets down there, it sort of pushes into the funnel and stays that way. Ultimately, these are theories. We’re not sure 100% why it might be. And we also don’t understand why some babies don’t end up head-down. Probably most of the time, it’s just luck that it just didn’t happen for that particular baby.

There are certain reasons it could be more likely. One of them that you mentioned was having an abnormal uterine shape. So, yes, there are some people who are born with an abnormally shaped uterus, maybe more like a heart, for example, or sometimes they have something called a unicornuate uterus, which is just one horn of a uterus. And that’s its own separate topic, abnormal uterine shapes. But that can happen. And when that happens, the babies don’t have the same space and room to sort of navigate into a head-down position, so there is a higher chance they won’t be head down.

Now you often would not know if you had an abnormal uterine shape before you got pregnant because it’s not… The testing that’s done to figure that out is not routinely done on people. You wouldn’t have any typical reason to have those imaging tests done before you get pregnant. And then when you deliver, if it’s by C-section, usually the surgeon would know if the uterus was shaped abnormally, not always, but usually. If you deliver vaginally, sometimes the obstetrician or midwife will know, sometimes not. And so it is possible for people to have one or two pregnancies and not know if their uterus is shaped abnormally.

If someone had a breech baby or several times they had a breech baby in several pregnancies, and they weren’t really sure, and it was not clear to me, maybe from the surgeon’s operative report, or it wasn’t us, sometimes I will recommend imaging to see if the uterus is shaped abnormally. That would either be a form of ultrasound called a saline infusion sonohysterogram or, sometimes, an MRI, and we can figure it out that way. There are other reasons. Sometimes, if there’s a low amniotic fluid, the baby can’t turn from breech to head down. Sometimes, if let’s say there’s a short umbilical cord or maybe it’s wrapped around the baby’s body or the baby’s neck several times, just sort of physically not allowing the baby to do that. But we don’t often know that until delivery.

So, the short answer to your question is I don’t know, but nobody knows. So, hopefully, since this was recorded after your delivery, I believe, hopefully, everything went well. Whether the baby turned and you had a vaginal delivery or whether you ended up with a C-section, I hope it went well. Sorry, I couldn’t give you a better answer to your excellent question.

Learn More on the Healthful Woman Podcast

Dr. Fox answers several other questions about breech births, gestational diabetes, PROM during a second delivery, gallbladder removal during pregnancy, and what to consider when having more children with a history of preclampsia. To learn more, listen to Mailbag 18 on the Healthful Woman podcast.

Maternal Fetal Medicine blogs are intended for educational purposes only and do not replace certified professional care. Medical conditions vary and change frequently. Please ask your doctor any questions you may have regarding your condition to receive a proper diagnosis or risk analysis. Thank you!