Single and Serial Fetal Biometry to Detect Preterm and Term Small- and Large-for-Gestational-Age Neonates: A Longitudinal Cohort Study

Abstract

ObjectivesTo assess the value of single and serial fetal biometry for the prediction of small- (SGA) and large-for-gestational-age (LGA) neonates delivered preterm or at term.MethodsA cohort study of 3,971 women with singleton pregnancies was conducted from the first trimester until delivery with 3,440 pregnancies (17,334 scans) meeting the following inclusion criteria: 1) delivery of a live neonate after 33 gestational weeks and 2) two or more ultrasound examinations with fetal biometry parameters obtained at ≤36 weeks. Primary outcomes were SGA (<5th centile) and LGA (>95th centile) at birth based on INTERGROWTH-21st gender-specific standards. Fetus-specific estimated fetal weight (EFW) trajectories were calculated by linear mixed-effects models using data up to a fixed gestational age (GA) cutoff (28, 32, or 36 weeks) for fetuses having two or more measurements before the GA cutoff and not already delivered. A screen test positive for single biometry was based on Z-scores of EFW at the last scan before each GA cut-off so that the false positive rate (FPR) was 10%. Similarly, a screen test positive for the longitudinal analysis was based on the projected (extrapolated) EFW at 40 weeks from all available measurements before each cutoff for each fetus.ResultsFetal abdominal and head circumference measurements, as well as birth weights in the Detroit population, matched well to the INTERGROWTH-21st standards, yet this was not the case for biparietal diameter (BPD) and femur length (FL) (up to 9% and 10% discrepancy for mean and confidence intervals, respectively), mainly due to differences in the measurement technique. Single biometry based on EFW at the last scan at ≤32 weeks (GA IQR: 27.4–30.9 weeks) had a sensitivity of 50% and 53% (FPR = 10%) to detect preterm and term SGA and LGA neonates, respectively (AUC of 82% both). For the detection of LGA using data up to 32- and 36-week cutoffs, single biometry analysis had higher sensitivity than longitudinal analysis (52% vs 46% and 62% vs 52%, respectively; both p<0.05). Restricting the analysis to subjects with the last observation taken within two weeks from the cutoff, the sensitivity for detection of LGA, but not SGA, increased to 65% and 72% for single biometry at the 32- and 36-week cutoffs, respectively. SGA screening performance was higher for preterm (<37 weeks) than for term cases (73% vs 46% sensitivity; p<0.05) for single biometry at ≤32 weeks.ConclusionsWhen growth abnormalities are defined based on birth weight, growth velocity (captured in the longitudinal analysis) does not provide additional information when compared to the last measurement for predicting SGA and LGA neonates, with both approaches detecting one-half of the neonates (FPR = 10%) from data collected at ≤32 weeks. Unlike for SGA, LGA detection can be improved if ultrasound scans are scheduled as close as possible to the gestational-age cutoff when a decision regarding the clinical management of the patient needs to be made. Screening performance for SGA is higher for neonates that will...

Second- to Third-Trimester Longitudinal Growth Assessment for the Prediction of Largeness for Gestational Age and Macrosomia in an Unselected Population

“…There are few reports about longitudinal (or serial) growth assessment for the prediction of LGA and macrosomia in unselected pregnancies, with conflicting results [10][11][12]. Hedriana and Moore [10] used averaged centiles from several ultrasound assessments between 28 and 42 weeks in 263 normal singleton pregnancies.…”

“…Salomon et al [11] assessed 356 normal singleton pregnancies for fetal growth potential (based on fetal biometry, fetal growth velocity [averaged z scores], and gestational age) and found that it can improve identification of fetuses at risk for late-onset growth abnormalities. A recent report by Tarca et al [12], in a large cohort of singleton pregnancies (n = 3,440), showed that longitudinal biometry calculated by linear mixed-effects models had lower sensitivities and did not provide additional information over cross-sectional measurement for predicting LGA (53 vs. 46% [p < 0.05] at ≤32 weeks). Nonetheless, as acknowledged by the authors, the main limitation of their study was that the number of scans varied among patients, making it difficult to rule out a selection bias whereby high-risk pregnancies are overrepresented.…”

Are selection criteria for healthy pregnancies responsible for the gap between fetal growth in the French national Elfe birth cohort and the Intergrowth‐21st fetal growth standards?

“…Our finding that the differences in growth parameters between the sample restricted to women fulfilling the IG selection criteria and the overall population were very small is relevant for the current debate on growth standards vs. references. It shows that population selection is not an explanation for the differences between the IG standards and fetal growth in the ELFE cohort and is also unlikely to explain the differences found in other population‐based studies . More broadly, this finding challenges the relevance of distinguishing between growth “references” and “standards” for fetal growth monitoring, at least in high‐income settings where malnutrition is low and access to health services is high.…”

A new customized fetal growth standard for African American women: the PRB/NICHD Detroit study

“…A comparison to the INTERGROWTH-21 st standard 16 was not performed due to differences in the ultrasound protocols that were previously noted 73 (eg the biparietal diameter was measured from the outer to the outer, while we measured from the outer to the inner, borders of the parietal bones) and also due to the different EFW formula used in the INTERGROWTH-21 st standard. Among the four standards compared in this study, there were significant differences in the fraction of fetuses classified as SGA (<10 th centile) based on the last available ultrasound examination for each pregnancy.…”

“…However, comparing how the in utero SGA and LGA screenings based on different standards relate to an SGA or LGA diagnosis at birth and to adverse pregnancy outcomes was outside the scope of the current study. Of note, the ability of ultrasound-based estimated fetal weight to predict actual birthweight was described previously 14, 29, 73 . For example, in a blinded study conducted in a low-risk population, Sovio et al 29 reported that an EFW<10 th centile at 36 weeks of gestation correctly identified 57% of fetuses (sensitivity) that were destined to have a birthweight <10 th centile, with a specificity of 95%.…”