Estimated fetal weight accuracy in pregnancies with preterm prelabor rupture of membranes by the Hadlock method

The accuracy of sonographic fetal weight in very preterm infants (≤32 weeks)

OBJECTIVE

To examine the accuracy of sonographic fetal weight to predict birthweight in very preterm infants (<32 weeks), and to compare the accuracy of estimated fetal weight (EFW) between those small for gestational age (SGA) and those appropriate for gestational age (AGA).

STUDY DESIGN

A retrospective study was conducted of data recorded between January 2010 and March 2023. Included were women with singleton livebirths at 23+0-31+6 weeks who had an EFW within one week from delivery. Mean percentage error, mean absolute percentage error, and underestimation and overestimation rates were calculated. We compared the accuracy of EFW between SGA and AGA infants.

RESULTS

In total, 360 women were included. The mean absolute percentage error was 7.8 % (range 0 %-68.9 %); for 207 (57.5 %) infants the percentage error was within ±10 %. Overestimation error >10 % was observed in 102 (28.3 %) infants and errors >20 % in 34 (9.4 %). Among infants born in the periviable period (23+0 - 25+6 weeks; N = 56), the mean absolute percentage error was 9.8 % (range: 0 %-40.3 %); the value was within ±10 % for only 28 periviable infants (50 %) and exceeded 20 % for 16.1 %. Among SGA compared to AGA infants, the mean absolute percentage error was higher (11.1% vs. 6.6 %, p = 0.035). Overestimation error >10 % was more frequent among SGA than AGA infants (55 (49.1 %) vs. 47 (19.0 %), p < 0.001). In a multivariate logistic regression analysis, SGA status was independently associated with a higher mean percentage error (beta = 0.260, p < 0.001) and an increased risk of an error >10 % (odds ratio = 2.1, 95 % confidence interval 1.2-3.5, p = 0.008).

CONCLUSIONS

Sonographic EFW is limited in assessing very preterm infants, particularly those who are SGA or born during the periviable period. These limitations should be considered regarding impending very preterm births and concerns about abnormal fetal growth.

Comparison of sonographic fetal weight estimation formulas in patients with preterm premature rupture of membranes

BACKGROUND

Estimation of fetal weight (EFW) by ultrasound is useful in clinical decision-making. Numerous formulas for EFW have been published but have not been validated in pregnancies complicated by preterm premature rupture of membranes (PPROM). The purpose of this study is to compare the accuracy of EFW formulas in patients with PPROM, and to further evaluate the performance of the most commonly used formula - Hadlock IV.

METHODS

A retrospective cohort study of women with singleton gestations and PPROM, admitted to a single tertiary center between 2005 and 2017 from 22^0/7-33^0/7 (n = 565). All women had an EFW within 14 days of delivery by standard biometry (biparietal diameter, head circumference, abdominal circumference and femur length). The accuracy of previously published 21 estimated EFW formulas was assessed by comparing the Pearson correlation with actual birth weight, and calculating the random error, systematic error, proportion of estimates within 10% of birth weight, and Euclidean distance.

RESULTS

The mean gestational was 26.8 ± 2.4 weeks at admission, and 28.2 ± 2.6 weeks at delivery. Most formulas were strongly correlated with actual birth weight (r > 0.9 for 19/21 formulas). Mean systematic error was - 4.30% and mean random error was 14.5%. The highest performing formula, by the highest proportion of estimates and lowest Euclidean distance was Ott (1986), which uses abdominal and head circumferences, and femur length. However, there were minimal difference with all of the first 10 ranking formulas. The Pearson correlation coefficient for the Hadlock IV formula 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 actual birth weight. This correlation was unaffected by gender (r = 0.936 for males, r = 0.932 for females, p < 0.001 for both) or by amniotic fluid level (r = 0.935 for mean vertical pocket < 2 cm, r = 0.943 for mean vertical pocket ≥2 cm, p < 0.001 for both).

CONCLUSIONS

In women with singleton gestation and PPROM, the Ott (1986) formula for EFW was the most accurate, yet all of the top ten ranking formulas performed quite well. The commonly used Hadlock IV performed quite similarly to Ott's formula, and is acceptable to use in this specific setting.

Detection of small for gestational age in preterm prelabor rupture of membranes by Hadlock versus the Fetal Medicine Foundation growth charts

Objective

The primary outcome was to compare the diagnostic accuracy of neonatal small for gestational age (SGA) by the Hadlock and Fetal Medicine Foundation (FMF) charts in our cohort, followed by the ability to predict composite severe neonatal outcomes (SNO) in pregnancies with preterm prelabor rupture of membranes (PPROM).

Methods

This study was a secondary analysis of a prospective cohort of pregnancies with PPROM from 2015 to 2018, from 23 to 36 completed weeks of gestation. Sensitivity, specificity, and positive and negative predictive values for the primary and secondary outcomes of the Hadlock and FMF fetal charts were calculated. The discriminatory ability of each chart was compared using the area under the receiver’s operating curves of clinical characteristics.

Results

Of the 106 women who met the inclusion criteria, 48 (45%) were screened positive using the FMF fetal growth chart and 22 (21%) were screened positive using the Hadlock chart. SGA was diagnosed in 12 infants (11%). Both fetal growth charts had comparable diagnostic accuracies and were statistically significant predictors of SGA (Hadlock: area under the receiver operating characteristic curves [AUC], 0.76, risk ratio [RR], 7.6, 95% confidence interval [CI], 2.5–23; and FMF: AUC, 0.76 RR, 13.3 95%CI 1.8–99.3). Both growth standards were poor predictors of SNO.

Conclusion

The Hadlock and FMF fetal growth charts have a similar accuracy to predict SGA in pregnancies complicated by PPROM. The FMF fetal growth chart may result in a 2-fold increase in positive screens, potentially increasing fetal surveillance.