Hmmm….

Recently, I wrote about the increased risk of placenta accreta or percreta due to a previous C-section. While the risk of placenta problems definitely increases exponentially for every previous Cesarean, there was something in the article that bugged me:

Studies and textbooks suggest that the risk of developing an accreta is as high as 40 percent in women who have had two previous Caesareans; that jumps to 60 percent with three C-sections, their physicians said.

Although I’m a strong proponent of vaginal birth, I do want to be truthful about C-sections, and I don’t think the above sentence is accurate. It just seems too high. Running some numbers — there are about 4 million births per year, and about 30% of them are C-section. I think that approximately 40% of annual C-sections are first-time sections, while the remaining 60% are repeat sections, or about 720,000. I haven’t looked it up, but I would hazard a guess that of the repeat surgical births, half of them are a second C-section, while the remainder would be a third or higher C-section. If the risk of accreta really were 40% after a second C-section, that would mean that 144,000 women would be at risk every year of developing placenta accreta. I just don’t think it’s that high. That would be 3.6% of all pregnant women developing accreta, or 36/1000. The article quotes current rates of accreta as ranging from 1/500-1/2,500 births, or 0.002-0.0004 — 18-90 times less than .036. So, even if some of my hypothetical numbers are wrong, there’s still plenty of wiggle room between “40-60% risk of developing placenta accreta” and 1/500-1/2,500.

Probably what happened is the reporter got confused, and misunderstood some of the literature. In trying to get to the bottom of this — to see if the risk of developing placenta accreta or percreta was really as high as the article quoted — I saw that there were numerous times when the phrase “placenta accreta/previa” was used. The gist of the articles and studies I read, was that when a woman has placenta previa (the placenta grows over the opening of the uterus — which is also more likely to happen after a prior Cesarean), then her risk of also developing placenta accreta is very high — along the lines of the percentages given in the quote. But if a woman does not have placenta previa, then her risk for placenta accreta — while it does increase exponentially with every C-section — does remain fairly low, and nowhere near the 40-60% risk solely due to past C-sections.

Another possible misunderstanding the author may have had was along these lines — finding that women who had accreta or percreta were much more likely to have had C-sections (which is very true), and getting the percentages or risks for that confused with the risks for developing accreta or percreta to start with. While I don’t know if this was the case, I have read many things (not just birth-related) in which journalists screwed up in a similar fashion. I’ll give you an exaggerated example of how easy it is to confuse matters, if you didn’t know any better:

Let’s say that about 86% of all women who choose home birth in the United States are both white and married. A journalist could easily get a bit muddled and report that in the United States, 86% of white, married women give birth at home. Since you and I are knowledgeable and educated birth junkies, we know that only about 1% of all births in America take place out of the hospital, so we would never be taken in by this misstatement. But others might. The two statements are very similar — an accurate percentage is given, and the details (home birth, white, married, United States, women) are all the same. But you can see the obvious difference between the two statements.

I should have caught the problem before I wrote my previous post; but since I didn’t, I wanted to clarify.

3 Responses

  1. I can’t comment on the statistics of placenta accreta with C/S. I just want to share an experience I had in the OR of a mom who was having her fourth C/S. I was waiting at the table in order to catch the baby. Before the OB could even cut through the uterus, a tiny little baby arm was waving at us from the mom’s abdomen. The mom’s uterus was so paper thin from all the previous C/S’s, that the baby broke through the uterus (aka:uterine rupture) to “wave” at us. It could have been a devastating outcome, but all was well. And, it was kinda cool to see.

  2. “Although I’m a strong proponent of vaginal birth, I do want to be truthful about C-sections, and I don’t think the above sentence is accurate. ”

    Thank you. I wish more folks had this desire.

  3. Good point. It didn’t hit me while reading the article, but that number IS too high. Nice catch!

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