Jan. 21, 2009 -- As the rate of cesarean deliveries in the USA has risen, so has the rate of rare but severe complications in mothers, researchers report today.
With more than a million performed annually, C-section is the country's most common operation. In 2006, the most recent year available, 31.1 percent of all U.S. births were C-sections, up 50 percent from 1998. While a number of studies have focused on C-sections' effects on newborns, few have looked at the effects on moms.
The new study, by government researchers, examined the rate of severe complications in women who delivered in U.S. hospitals in two time periods: 1998-99 vs. 2004-05.
They found a 90 percent increase in blood transfusions and a 50 percent increase in pulmonary embolisms, or blood clots in the lungs. They also found about a 20 percent increase in rates of kidney failure, respiratory distress syndrome, shock and the need for a ventilator.
While the study doesn't prove that C-sections cause complications, tracking those complications could be useful, says co-author Susan Meikle, a medical officer at the Eunice Kennedy Shriver National Institute of Child Health and Human Development.
The actual number of deliveries with at least one complication was 0.64 percent in 1998-99 and 0.81 percent in 2004-05. "Even though the absolute numbers are low, the rates are increasing. ... We could do a better job at tracking these complications," says Meikle, an obstetrician. "There may be short-term trade-offs and long-term trade-offs (depending on mode of delivery). We don't know that yet."
Although the average age of women giving birth has been rising, that didn't seem to play a big role in the complication rates, the researchers write in the Journal of Obstetrics & Gynecology. But they found that the rising cesarean rate seemed to explain the hikes in kidney failure, respiratory distress syndrome and ventilation. The rise in C-sections only partially contributed to increases in shock, pulmonary embolisms and transfusions.
The authors lacked information about race and whether the women were overweight, both of which could impact the risk of complications. They also didn't know why C-sections were performed and whether moms who had them were sick beforehand.
The study used the largest U.S. inpatient care database, which in 2005 sampled hospitals from 37 states, constituting about 90 percent of hospital discharges in the country.
Michael Kramer, scientific director of the Canadian counterpart of Meikle's institute, notes that in some cases, a complication might have triggered a C-section, not vice-versa. Still, says Kramer, co-author of a 2007 report that found more severe maternal complications in planned C-sections than in vaginal deliveries, doctors tend to underestimate C-section risks.