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.