by Heidi Green
June 11, 2008

Can you believe it? In 2005, nearly one in three births were delivered by primary or repeat cesarean section. One in three. That’s a whopping 1.2 million births, and it makes c-sections the most common surgical procedure for women in the United States (U.S.).

How about this? In 2005, nearly one in eight births were preterm (before 37 weeks). Preterm birth is the top contributor to neonatal morbidity and mortality in the U.S.

For this reason, the American College of Obstetricians and Gynecologists cautions against elective induction and c-section before 39 weeks. Still, recent increases in the rate of preterm births were due to increases in late preterm (34–36 week) births and in medically indicated preterm birth. In short, increases in obstetric interventions seem to be causing infants to be born sooner.

A recent study by researchers from the March of Dimes, Albert Einstein College of Medicine, and the Centers for Disease Control and Prevention sought to explore the relationship between c-sections and the trend towards lower gestational age. They looked at those U.S. births in which only one infant was born, excluding twin and other multiple-child births that are prone to preterm delivery. They also focused on data through 2005.

Among the findings:

• C-section rate increased 46 percent between 1996 and 2005. The main cause was a rise in the number of first-time mothers having c-sections; odds are great these women will have c-sections for later pregnancies, too.

• C-section rates for mothers of all races/ethnicities climbed. Non-Hispanic black, non-Hispanic white, and Hispanic mothers were all affected.

• Late preterm birth rate rose more than 44 percent between 1981 and 2005, to 9.1 percent. Late preterm births are the fastest growing subgroup of preterm births; increases have been shown to be related, on part, to increased medical interventions.

• Preterm birth rate varies by race/ethnicity. In 2005, non-Hispanic black infants were nearly twice as likely to be born preterm as non-Hispanic white and Hispanic infants.

• Evidence is mounting about adverse outcomes associated with late preterm births. These outcomes can affect both the infants and, in the case of c-sections, mothers.

The researchers suggest that two clinical questions be addressed when intervention before term is being considered: Is delivery necessary? And, if so, what delivery route should be used?

Expectant mothers and their health care providers are urged to consider the risks of preterm birth versus the risks of continuing a pregnancy.