Survival and neonatal morbidity among extremely preterm born infants in relation to gestational age based on the last menstrual period or ultrasonographic examination.

OBJECTIVES The aim of this study was to investigate the potential impact of gestational age (GA) estimation on the basis of the last menstrual period (LMP) in comparison with GA based on ultrasound examination on rates of survival and neonatal morbidity among extremely preterm infants. METHODS The Swedish national registry of infants born extremely preterm (Extremely Preterm Infants in Sweden Study), including infants born before 27 weeks of gestation, was used to identify 645 infants with available information. Incidences of stillbirth, survival, small for GA (SGA), and major neonatal morbidity were calculated in relationship to the GA estimated by each of the approaches. RESULTS Pregnancies, in general, appeared to be longer when GA was estimated by LMP than by ultrasound (17.2% of the pregnancies were longer than 27 weeks). The incidences of stillbirth, neonatal death, and major neonatal morbidity in relationship to GA were similar for both groups. The risks for SGA were elevated when GA according to ultrasound examination was at least 7 days shorter than GA based on the LMP. CONCLUSIONS In our cohort of infants born extremely preterm, estimation of GA on the basis of LMP indicated a longer pregnancy than estimated by ultrasound but did not influence the incidences of neonatal survival and morbidity.