Another way to determine who gets C-sections

BOSTON -- Doctors who use age, weight and other factors to predict if a pregnant woman will need a Caesarean section to deliver her baby have a new gauge: the length of the cervix, researchers say.

The cervix closes off the uterus, where the baby is growing. Researchers in Britain say their study of more than 27,000 pregnancies found that women with the longest cervixes were more likely to need surgery to deliver their child.

The C-section rate was 25.7 percent for women with a cervix between 40 and 67 millimeters, 21.7 percent for 36 to 39 millimeters, 18.4 percent for 31 to 35 millimeters and 16 percent with a cervical length of 16 to 30 millimeters. An inch is about 25 millimeters.

"Rates of Caesarean delivery started to rise at a cervical length of 25 millimeters and plateaued at a cervical length of 50 millimeters, approximately doubling across the range of observed values," said the team led by Dr. Gordon Smith of Cambridge University.

"These findings suggest that cervical length at mid-pregnancy is an important indicator of the risk of primary Caesarean delivery at term."

Studies had previously shown that a short cervix increased the risk of premature birth.

Eight hospitals in and around London participated in the study, published in the New England Journal of Medicine. Length was measured with ultrasound in the 22nd, 23rd or 24th week of pregnancy.

The proportion of babies delivered by C-section has increased dramatically in recent decades in the United States and many other countries.