Discrepancy between pregnancy dating methods – correlates and outcomes

Abstract: With the introduction of obstetric ultrasound there has been a shift from last menstrual period-based to ultrasound-based estimation of gestational age. The choice of the method and timing of pregnancy dating is important because it can affect dating precision and perinatal outcomes.First, when comparing two large population-based cohorts from the Medical Birth Register, from before and after the introduction of ultrasound-based pregnancy dating, male infants on the edge of prematurity did not benefit from progress in medical care as much as female infants in terms of prematurity-related outcomes. This might reflect a bias introduced by the ultrasound-based pregnancy dating method, because of a tendency to overestimate gestational age in pregnancies with a male fetus.Second, in a large population-based cross-sectional study, the associations of discrepancies between last menstrual period-based and ultrasound-based estimates with variables such as fetal sex and maternal height, indicated that ultrasound-based pregnancy dating introduced systematic errors presumably related to the method’s use of fetal size as a proxy for gestational age. The largest effect estimates were found for maternal obesity in cases of large negative discrepancies.Third, in a large population-based cohort study, discrepancies between last menstrual period-based and ultrasound-based estimates were associated with several adverse pregnancy, delivery, and neonatal outcomes. Most importantly, a large negative discrepancy was associated with higher odds for neonatal and intrauterine fetal death, as well as for an infant being small for gestational age.Fourth, in a survey study there was overall good adherence to national guidelines, except for early pregnancy dating. However, the management of discrepancies between methods for pregnancy dating varied widely in clinical practice, which may be due to the lack of national guidelines.In summary, ultrasound-based dating can be biased by maternal or fetal characteristics. Discrepancies between methods for pregnancy dating may indicate a need for closer monitoring to optimize perinatal care during pregnancy and childbirth.