Increased risk of perinatal/neonatal death in infants who were smaller than expected at ultrasound fetometry in early pregnancy.

Objectives: To investigate if there is an association between perinatal/neonatal death and a discrepancy between gestational age by ultrasound fetometry in early pregnancy (GA(U)) and gestational age by last menstrual period (GA(LMP)), and to investigate possible causes for such an association.

Methods: The Swedish Medical Birth Registry was used to identify singleton pregnancies with information available on GA(LMP) and GA(U) that were delivered in Sweden between 1990 and 2000. A total of 718 011 pregnancies was included and information on the pregnancy and delivery was obtained from the National Board of Health.

Results: Infants with a GA(U) at least 7 days less than the GA(LMP) were at increased risk for stillbirth (odds ratio (OR), 1.45; 95% CI, 1.32-1.58), neonatal death within 1 month (OR, 1.87; 95% CI, 1.67-2.09), Apgar score < 7 at 5 min (OR, 1.18; 95% CI, 1.11-1.24), birth weight < 2500 g (OR, 1.48; 95% CI, 1.43-1.52), and preterm birth < 37 weeks (OR, 1.45; 95% CI, 1.42-1.49). The association between a postponed expected date of delivery and perinatal/neonatal death increased with gestational length and was especially pronounced among infants who were born after at least 40 completed weeks of pregnancy (GA(U)).

Conclusions: A discrepancy between GA(U) and GA(LMP) may indicate early disturbances in fetal/placental development. Furthermore, it can be speculated that, as the risk significantly increased with gestational duration, at least a part of the increased risk for poor pregnancy outcome in adjusted pregnancies was due to consequences of true post-term pregnancies not being recognized as such.