Early dating by ultrasound and perinatal outcome

BACKGROUND: This study aims to evaluate the impact of routine ultrasound in early pregnancy on pregnancy outcome and perinatal mortality. METHODS: Using the Swedish Medical Birth Registry, a two-stage study was designed. First, an ecological study that included data from 45 hospitals, with 1,280,746 children born during the years 1974-1991, was designed by differentiating hospitals on the basis of ultrasound usage. Second, a historical cohort study (n = 60,864) was designed for the years 1982-84, including a treatment group (having had routine ultrasound in early pregnancy) and a reference group (having had no routine ultrasound). RESULTS: In hospitals practicing early dating by ultrasound, post-term births were reduced from 13.3% to 7.4%, while pre-term births were increased from 5.7% to 6.8%. For the treatment group, the cohort study showed: 1) fewer post-term births, RR 0.7 (95% CL 0.7-0.8), 2) lower post-term perinatal mortality, RR 0.3 (95% CL 0.1-1.0), 3) fewer twin births post-term, RR 0.1 (95% CL 0.1-0.7), 4) fewer acute growth retarded among term, RR 0.7 (95% CL 0.6-0.9) and post-term, RR 0.3 (95% CL 0.1-1.1), and 5) a tendency towards less asphyxia among post-term births. CONCLUSION: The study shows that early dating with ultrasound increases the possibilities of clinical judgment at the end of the pregnancy and also indicates that the procedure could contribute to a positive perinatal outcome.