# Concordance Between Estimated Fetal Weight by Ultrasound and Birth Weight and Its Association with Adverse Perinatal Outcomes

## TL;DR

This study found that estimated fetal weight from ultrasounds often doesn't match actual birth weight, and this mismatch is linked to worse outcomes for mothers and babies.

## Contribution

The study identifies that inadequate fetal biometry measurements and timing of ultrasounds are linked to adverse perinatal outcomes.

## Key findings

- Inadequate fetal biometry measurements were common, especially for abdominal circumference.
- Estimated fetal weight was a strong predictor of macrosomia (birth weight >4000 g).
- Ultrasounds performed 7 days before delivery were linked to higher risk of adverse outcomes.

## Abstract

Objective: The aim of this study was to analyze the concordance between estimated fetal weight (EFW) and birth weight among ultrasound examinations with fetal biometry considered adequate and inadequate according to the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) guidelines, and its association with adverse perinatal outcomes. Methods: This was a retrospective and cross-sectional study carried out in two centers, involving parturients who delivered between 37 and 41 weeks. The following parameters were evaluated: biparietal (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) measurement; EFW; the interval between the ultrasound and delivery; and the discrepancy between EFW and birth weight. A minimum of 140 participants were required to assess the association between EFW and birth weight. Results: A total of 305 ultrasound examinations were selected and divided into two groups: adequate (Group I n = 115) and inadequate (Group II n = 190) fetal biometry. The measurements of the cephalic pole (BPD + HC), AC, and FL were inadequate in 69.5% (132/190), 91.6% (175/190), and 72.1% (137/190) of participants, respectively. Group I had a lower gestational age at ultrasound examination (38.4 vs. 39.9 weeks, p < 0.001), a larger BPD measurement (93.9 vs. 91.6 mm, p = 0.001), a longer interval between ultrasound examination and delivery (3.8 vs. 2.0 days, p < 0.001), and a smaller discrepancy between EFW and birth weight (7.2 vs. 9.5%, p = 0.002) than Group II. In Group I, EFW was a strong significant predictor (AUC:0.94, 95%CI 0.85–0.99, p = 0.032) for identifying birth weight >4000 g. An EFW cut-off value of 4019.0 g was found to be a correct identifier for 85.7% of newborns with a birth weight >4000 g, with a false-positive rate of 13.7%. Group I had a lower risk of postpartum hemorrhage (7.0% vs. 15.8%, OR:0.39, 95%CI 0.17–0.90, p = 0.024) and composite adverse perinatal outcomes (13.0 vs. 23.3%, OR:0.49, 95%CI 0.26–0.94, p = 0.030) than Group II. In Group I patients, undergoing an ultrasound 7 days before delivery was an independent predictor of composite adverse perinatal outcomes [x2(1) = 4.9, OR:0.49, 95%CI: 0.26–0.94, R2 Nagelkerke:0.026, p = 0.030]. Conclusions: We observed a high rate of inadequate fetal biometry. There was poor concordance between EFW and birth weight. EFW was a strong significant predictor for identifying macrosomia. Ultrasound examination performed 7 days before delivery was an independent predictor of adverse perinatal outcomes.