Routine ultrasound screening in the third trimester: a population-based study

Background No population-based study has evaluated the effects of third trimester ultrasound screening on prognosis. Objective. To study the effects of routine ultrasound screening in the third trimester on perinatal/infant mortality, prevalence of small for gestational age infants (SGA) and low Apgar score. Study design. Two university clinics using routine ultrasound screening in the third trimester were compared with seven county or district hospitals with no routine screening. Deliveries between 1985 and 1996 were included. In all, 16 municipalities including 56 371 pregnancies with routine screening were compared with 59 municipalities and 153 355 pregnancies without third trimester screening. An observational design was applied, using data stored during pregnancy, delivery, and during the first year (infant mortality) at the Swedish Medical Birth Registry, The National Board of Health and Welfare. Odds ratio with 95% confidence interval was used in the evaluation. End-points included incidence of SGA, perinatal/infant mortality, Apgar score at 5 min, cesarean section and instrumental delivery in areas with versus without routine third trimester screening Results. No significant difference was seen in the prevalence of the most extreme SGA (< -3 SD from the mean), perinatal complications including cesarean section or instrumental delivery, or perinatal/infant mortality between units with versus without routine ultrasound screening in the third trimester. Conclusion. Added to the findings of previous small randomized studies, it seems as if routine third trimester ultrasound screening in an unselected population does not reduce perinatal mortality or early neonatal morbidity, expressed as Apgar scores or SGA.