The number of baby boys getting circumcised in hospitals has dropped slightly in the past decade, health experts said on Thursday.

Researchers at the U.S. Centers for Disease Control and Prevention analyzed data from three national surveys to track changes in hospital rates of circumcision, which involves removing the foreskin of the penis.

In one survey, newborn male circumcision rates fell to 56.9 percent in 2008 from 62.9 percent in 1999. In another, rates of circumcision fell to 54.7 percent in 2010 from 58.4 percent in 2001. In a third, rates fell to 56.3 percent in 2008 from 63.5 percent in 1999.

The CDC said the figures likely underestimated the actual rate of circumcisions because they did not include circumcisions performed within communities.

Circumcision is a ritual obligation for infant Jewish boys, and is also a common rite among Muslims, who account for the largest share of circumcised men worldwide.

The wider U.S. population adopted the practice due to potential health benefits, but those advantages have become the subject of debate, including a recent effort to ban circumcision in San Francisco.

CDC researchers noted three recent studies that have shown that male circumcision decreases transmission of the HIV virus that causes AIDS.

Male circumcision has also been shown to cut the risk of herpes, human papillomavirus or HPV infections and genital ulcer disease in men, and also HPV infection, trichomoniasis, and bacterial vaginosis and genital ulcer disease in their female partners.

Critics say the surgery exposes infants to pain unnecessarily. In San Francisco, opponents fought hard to add a ballot measure banning the practice to the city’s November ballot. Statewide efforts are under way to block such bans.

Researchers at the CDC said the recent 10-year decline in circumcisions in U.S. hospitals followed a sharp increase in the prior 10-year period. Circumcision rates rose to 61.1 percent from 1997 to 2000 from 48.3 percent in 1988.

“Many factors likely influence rates of newborn male circumcision,” CDC researchers said in a weekly report on death and disease.

Medicaid coverage may be one factor. A recent study found circumcision rates were 24 percentage points higher in states in which it was routinely paid for compared with hospitals in states that do not cover the procedure.

As of 2009, Medicaid paid for circumcision in 33 U.S. states.

SOURCE: Morbidity and Mortality Weekly Report, September 2, 2011.