Rising infant mortality rates linked to increase in preterm, cesarean deliveries

September 1, 2011

Preterm birth exerts a huge influence on infant mortality, and because less than half of preterm births are linked to spontaneous labor, it's important to consider the possible effect of obstetric intervention on the preterm birth rate.

Preterm birth exerts a huge influence on infant mortality, and because less than half of preterm births are linked to spontaneous labor, it's important to consider the possible effect of obstetric intervention on the preterm birth rate, an expert from the National Center for Health Statistics (NCHS) said recently.

"In 2000, 34.6% of all infant deaths were preterm related. By 2007 this had increased to 36.0%," Marian MacDorman, PhD, told the Health and Human Services Secretary's Advisory Committee on Infant Mortality.

The US preterm birth rate increased by 36% in 18 years, from 9.4% to 12.8% in 2006, MacDorman said. The rate declined to 12.2% in 2009, but it is still much higher than in a number of other nations.

Cesarean rates for singleton births were higher for earlier gestational ages. For example, in 2006, 47% of births before 32 weeks were cesarean deliveries, compared with 42% of those at 32 to 33 weeks, and 34% at 34 to 36 weeks.

Over the same years, the percentage of singleton preterm births by induced labor doubled, from 8% to 16%. However, those figures might be conservative because induction of labor may be underreported.

MacDorman said that several major health insurance groups have taken steps to limit or prohibit medically elective cesareans before 39 weeks; although it's too soon to know the effect of these programs, the recent decline in the percentage of preterm births is encouraging.

In other discussion, MacDorman noted that in international rankings for infant mortality, the United States fell from 12th in 1960 to 30th in 2005. (MacDorman's presentation preceded the World Health Organization's recent report that said that the United States had fallen in 2009 to 41st among nations in terms of neonatal mortality.)

Researchers have noted that some of this country's lower ranking may be explained by the differences in how nations report live births and perinatal deaths.

Noting that the US percentage of preterm births is much higher than in Europe, MacDorman said, "If the United States had the same gestational age distribution as Sweden's, the US infant mortality rate would fall from 5.8 to 3.9 infant deaths per 1,000 live births."

NCHS statistics show that there still are huge differences in infant mortality by the mothers' race and ethnicity. Also surprising is that across most racial and ethnic groups, infant mortality was higher for mothers born in the United States than for those born elsewhere.