Objective To analyse the effectiveness of antenatal care as a screening for nonsymptomatic disease and obstetrical risk conditions.

Design Programme evaluation of antenatal care in a geographically based cohort.

Setting Routine clinical practice in primary and specialist level of health care without intervention, Subjects One thousand nine hundred and eight women residing in one Norwegian county giving birth during a 12 month period, 1988 to 1989.

Outcome measures The detection rates at the time of delivery, for women with five conditions: twin pregnancies, placenta praevia, breech presentation, small for gestational age (SGA) and pre-eclampsia.

Results Two hundred and ninety-two women had one or more of the actual conditions, 124 (42%) had been diagnosed at the time of the delivery.