Estimation of gestational maturity of preterm infants by five fetal sonographic measurements compared with neonatal EEG and the last menstrual period

Abstract

We previously reported no differences in estimates of gestational maturity between a cumulative score based on sonography/obstetrical measurements and an EEG interpretation for healthy preterm neonates. For the present study, a rank order among 5 fetal sonographic measurements was used to estimate gestational age: head circumference, transcerebellar diameter, biparietal diameter, femur length, and abdominal circumference were compared with an electroencephalographic estimate and an arithmetic estimate of maturity (i.e., the mother's last menstrual period). A fetal sonographic study for each of 13 premature neonates (i.e., born at < 32 weeks estimated gestational age) was followed after birth by a neonatal EEG recording. EEG and sonographic estimates of maturity were assigned without knowledge of other clinical data. The mother's last menstrual period was obtained from the medical record. Principal component analysis determined that 86% of the variance was evenly distributed over the 5 sonographic measurements. Using a regression procedure, 61 % of the variance (adjusted r 2 = 0.61) was explained by EEG when compared with fetal sonographic estimates. Only 19% (adjusted r 2 = 0.19) of the variance was explained by the estimate based on the mother's last menstrual period. Optimal subset selection determined that the rank order for prediction of gestational maturity among the fetal sonographic measurements was as follows: (1) head circumference; (2) transcerebellar diameter; (3) biparietal diameter; (4) femur length; (5) abdominal circumference. Cranial measurements on fetal sonography (i.e., head circumference, transcerebellar diameter, biparietal diameter) compared more closely with EEG estimates than non-cranial measurements (i.e., femur length and abdominal circumference). In conclusion, neonatal EEG estimates of gestational maturity compared more closely with sonographic measurements than estimates based on the time of the last menstrual period. These findings will be useful in situations when dates of conception are unknown or inaccurate, or when intrauterine growth restriction causes discrepancies in growth rates between cranial and non-cranial fetal measurements on sonography.