Accuracy of Hadlock IV and fetal weight estimation in preterm premature rupture of membranes

Abstract

<h3>Objectives</h3> Estimated fetal weight (EFW) helps inform clinical decision making in patients with preterm premature rupture of membranes (PPROM). The Hadlock IV formula is the most commonly used calculation of EFW using biparietal diameter, head circumference, abdominal circumference, and femur length. The study objective was to assess the accuracy of the Hadlock IV calculation in patients with PPROM. <h3>Methods</h3> We performed a retrospective cohort study of singleton gestations with PPROM admitted between 22⁰–33⁰ weeks gestational age (GA) to a single, university-affiliated, tertiary hospital between 2003–2017. All women had a sonographic EFW performed within 14 days of delivery calculated by Hadlock IV formula. The Pearson correlation was calculated to determine the association between EFW and birthweight (BW). <h3>Results</h3> Five-hundred-sixty-five women were included. Mean GA was 26.8±2.4 at admission, and 28.2±2.6 at delivery. The median EFW-to-delivery interval was three days (0–14 days, intraquartile range 5 days), mean BW 1154±418 grams, and mean EFW 1078±382 grams. Overall, 49.4% of women had maximal vertical pocket (MVP) <2cm at time of EFW. The Pearson correlation coefficient between EFW and BW was strong at r=0.935 (p<0.001), with 319 (56.5%) of measurements falling within 10%, 408 (72.2%) within 15%, and 455 (80.5%) within 20% of BW. This correlation was not affected by gender (r=0.932 for females, r=0.936 for males, p<0.001 for both) or by level of amniotic fluid (r=0.935 for MVP<2 cm, r=0.943 for MVP≥2cm, p<0.001 for both). <h3>Conclusions</h3> The study shows that Hadlock IV provides an accurate EFW in patients with PPROM, regardless of fetal sex or amniotic fluid levels.