Changes in maternal characteristics and obstetric practice and recent increases in primary cesarean delivery

OBJECTIVE: To estimate the contribution of changes in maternal characteristics (namely, age, parity, prepregnancy weight, weight gain in pregnancy, smoking status) and obstetric practice (namely, labor induction, epidural anesthesia, delivery by an obstetrician, midpelvic forceps delivery) to recent increases in primary cesarean delivery rates. METHODS: We studied all deliveries in Nova Scotia, Canada, between 1988 and 2000 after excluding women who had a previous cesarean delivery (n = 127,564). Logistic regression was used to study the effect of changes in maternal characteristics and obstetric practice on primary cesarean delivery rates. The effect of changes in midpelvic forceps delivery was examined through ecologic Poisson regression. RESULTS: Primary cesarean delivery rates increased from 13.4% of deliveries in 1988 to 17.5% in 2000. This was due to increases in cesarean deliveries for dystocia (14% increase), breech (24% increase), suspected fetal distress (21% increase), hypertension (47% increase), and miscellaneous indications (73% increase). Adjustment for maternal characteristics reduced the temporal increase in primary cesarean delivery rates between 1988-1991 and 1998-2000 from 21% (95% confidence interval CI 16%, 25%) to 2% (95% CI -2%, 7%). Additional adjustment for obstetric practice factors further reduced period effects. Midpelvic forceps delivery was significantly and negatively associated with primary cesarean delivery (P =.001). CONCLUSION: Recent increases in primary cesarean delivery rates are a consequence of changes in maternal characteristics. Obstetric practice, which has altered due to changes in maternal characteristics and concerns related to fetal and maternal safety, has also contributed to increases in primary cesarean delivery.