Epidemiologic predictors of cesarean section in nulliparous patients at low risk. RADIUS Study Group. Routine...

We sought to determine whether certain maternal and fetal characteristics influenced the risk of maternal- and fetal-indicated cesarean sections in pregnant women at low risk for adverse perinatal outcomes.

From a cohort of 6393 low-risk nulliparous patients maternal and fetal indicated cesarean section rates with 95% confidence intervals were calculated and stratified by demographic, anthropometric, and clinical tests and measurements. The strongest risk factors were modeled by means of multiple logistic regression.

Few risk factors distinguished maternal from fetal characteristics preceding cesarean delivery. Maternal age was associated with increased cesarean section risk in the tallest group of women only, and cesarean section rates decreased with increasing height, increased with higher prepregnancy weights, and was highest in women carrying male fetuses. Higher first prenatal visit diastolic blood pressure, increasing numbers of nonstress tests, > or = 2+ prenatal urine protein, late sonograms, geographic region, and practice type were statistically significant risk factors as well. Interestingly, results of prenatal visit tests and measurements contributed less to the prevalence of cesarean section than did age, fetal sex, and anthropometric parameters. However, the generalizability of these results is limited to low-risk (predominantly white) populations.

Of the risk factors we were able to assess, a large proportion of the incidence of cesarean section in this population of nulliparous patients at low risk was attributable to age, sex of fetus, and anthropometric patient profiles.