Why Understanding Statistics Matters
People like to say that statistics lie. Actually, the statistics tell the truth, people just are not always educated to understand what they mean. This happens alot in the birth world with the cesarean rate.
The CDC releases statistics about birth in the United States each year. In 2010, the CDC reported that 32.8% of all births in the United States were by cesarean surgery. This data has lead some childbirth professionals to assume a woman giving birth in the US has about a 33% chance of ending up with a cesarean. But this isn’t necessarily true. Why?
Because that number includes two different groups of women with two different rates of cesarean surgery.Childbirth Connection has a graph that may help visual learners get this concept, and statistics nerds may prefer this 2005 report from the CDC.
One group of women in that number is women who either never gave birth or only gave birth vaginally. The other group of women in the number is women who previously gave birth via cesarean. Women with a previous cesarean may give birth vaginally, or via cesarean. Currently the VBAC rate in the United States is pretty low, which means the cesarean rate for women who previously gave birth via cesarean is pretty high.
As you look at the graphic on the Childbirth Connection page, notice how in 1989, the cesarean rate was about 23%. Using this graphic we see that about 18% of women who had a cesarean previously gave birth vaginally, which means about 82% of those women gave birth via cesarean. In the same year about 16% of women who had never had a cesarean before gave birth via cesarean. Although the overall rate was 23%, a woman who had never had a cesarean before only had a 16% chance of having a cesarean.
Fast forward to 2004 on the Childbirth Connection graphic and you see the rate of cesarean increased to about 29%. Rate of VBAC declined to about 9%, meaning about 91% of women with a prior cesarean gave birth via cesarean. Primary cesarean rate also increased, but to about 19%. So although the overall rate of cesarean was 29%, only 19% of women without a prior cesarean gave birth via cesarean.
The graphic stops at 2005 because of implementation of a new birth certificate system which prevents accurate counting, but we can estimate as long as we accept the numbers we have are only estimates. In 2010, 33 states were using a birth certificate that allows us to count primary cesareans. So we have a count, but it will miss about 25% of the births in the country (because they happened in one of the 17 other states).
From the data we have, we can estimate that in 2010, 23.6% of women without a prior cesarean gave birth by cesarean while about 91% of women who previously gave birth via cesarean did so again. This means, that although the overall rate of cesarean in 2010 was 32.8%, a woman giving birth for the first time had a 23.6% chance of having a cesarean. Instead of 1 in 3, her chances are more like 1 in 4.5. On the flip side, 9 in 10 women with previous cesarean are likely to give birth via cesarean.