Accuracy of fetal weight estimation with regard to clinical decision making in preterm birth at the limit of viability

Objective: To identify possible confounding factors that have a negative impact on the accuracy of fetal weight estimation (FWE) in very low gestational age infants and to determine the impact of the accuracy of FWE on neonatal outcome.

Methods: In this retrospective study, we included 87 cases from 23 – 26 weeks of gestation at birth that were further divided into three groups (accurate, overestimated and underestimated birth weight). 12 factors that potentially influence the accuracy of FWE (gestational age, gender, use of antenatal corticosteroids, multiple pregnancy, presentation of fetus, location of placenta, AFI, rupture of membranes, contractions, time interval between estimation and delivery, examiners grade of experience, maternal BMI) were analyzed for each group. Differences in risk of overall neonatal death were calculated with estimated and actual birth weight (BW) and compared for each group.

Results: In 54 (62.1%) cases, FWE was accurate to birth weight. Compared to accurately estimated infants, male gender, anterior location of placenta and oligohydramnios was significantly different in underestimated infants. The risk of death was underestimated by 11.3% when BW was overestimated, whereas it was overestimated by 8.8% in the underestimated BW group and only 3.4% in the accurate BW group.

Conclusions: Gender, location of placenta, AFI and the time interval between estimation and delivery appear to have an effect on the accuracy of FWE. Inaccurate weight estimation leads to significant miscalculations of the risk of fetal death and might therefore negatively affect physicians' and parents' decision regarding the treatment.