The likelihood that a pregnant woman will have to undergo an unplanned c-section delivery after starting labor can be predicted by four parameters, British researchers have shown.

Dr. Elisabeth Peregrine and colleagues at the University College London Hospitals studied 267 women at 36 weeks gestation or later who were scheduled for induction of labor. Eighty women (30 percent) ended up having an emergency cesarean.

Of all the measures assessed, four factors in particular were strongly tied to the need for a c-section.

Having never had a previous pregnancy raised the chances 20-fold. A body mass index over 30 (obese) was tied to 6-fold greater risk, while being tall reduced the chances slightly. Finally, a longer cervix measured by ultrasound was associated with a higher chance of having a cesarean.

When these factors were considered together they were “reasonably” accurate in predicting who would undergo a cesarean, Peregrine’s team reports in the medical journal Obstetrics and Gynecology.

Maternal height and BMI “have been known for a while to influence the risk of cesarean section,” Peregrine explained. “However it has been difficult to quantify them and combine them together to provide the woman with useful advice.”

She also pointed out that measurement of cervical length by ultrasound is not done routinely at the moment, so the obstetrician in routine practice would not have this information.

Before the study’s findings can be used to counsel women, they need to be validated, she added, and that is under way. If the results prove accurate, women could be told their risk of having an emergency cesarean delivery - and those at high risk could be offered the chance to have a planned c-section.

SOURCE: Obstetrics and Gynecology, February 2006.