Is Sonographic Assessment of Fetal Weight Influenced by Formula Selection?

Objective. Several published formulas exist for the determination of estimated fetal weight (EFW), with limited data on their comparative accuracies. The aims of our study were to assess and compare the performance of different EFW formulas in predicting actual birth weight (BW) in an urban population. Methods. Patients with an EFW determined within 7 days of delivery were considered eligible for the study. Fourteen published formulas, derived from populations comparable to ours, were used to recalculate EFWs from the same initial measurements. The accuracy of the EFWs obtained from the different formulas were compared by percentage error methods using bias and precision and Bland‐Altman limits of agreement methods. Sensitivity and specificity for prediction of being small for gestational age (SGA) were calculated. Results. Eighty‐one fetuses were included in the study. Formula C of Hadlock et al [Hadlock C; log₁₀ BW = 1.335 ? 0.0034(abdominal circumference [AC])(femur length [FL]) + 0.0316(biparietal diameter) + 0.0457(AC) + 0.1623(FL); Am J Obstet Gynecol 1985; 151:333–337] had the best performance according to the bias and precision method. Bland‐Altman limits of agreement confirmed these results. Among the formulas, the sensitivity for detection of SGA ranged from 72% to 100%, and specificity was 41% to 88%. Hadlock C had the optimal sensitivity/specificity trade‐off for detection of SGA. Conclusions. Fourteen formulas showed considerable variation of bias and precision in our population as well as a wide range of sensitivities and specificities for SGA. The choice of the appropriate formula for EFW in a given population should be based on objective and explicit criteria. Consideration of bias and precision for the formula in the population being assessed is critical and may affect clinical care.     

Association of Crown‐Rump Length at 11 to 14 Weeks' Gestation and Risk of a Large‐for‐Gestational‐Age Neonate

Objective. The purpose of this study was to evaluate the association between crown‐rump length (CRL) and the risk of a large‐for‐gestational‐age (LGA) neonate. Methods. Data were retrospectively collected on consecutive women with a healthy singleton pregnancy followed to delivery at our center from 2003 to 2006 who underwent nuchal translucency, pregnancy‐associated plasma protein‐A, and free β‐human chorionic gonadotropin screening at 11 to 14 weeks' gestation. Pregnancies were dated by the last menstrual period (LMP) confirmed by CRL at 6 to 10 weeks or the known time of fertilization. The fetal CRL at 11 to 14 weeks was obtained from frozen sonographic images. The measured CRL was converted to gestational weeks using the method of Hadlock et al (Radiology 1992; 182:501–505). The expected gestational age (GA) by the LMP was subtracted from the measured GA to yield the ΔCRL. The association between the ΔCRL and birth weight was statistically analyzed. Results. The sample included 521 women. Fifty neonates (9.6%) were LGA (≥90th percentile), 38 (7.3%) small for gestational age, and 433 (83.1%) appropriate for gestational age. The LGA group was characterized by significantly larger‐than‐expected CRL measurements (P = .033). The birth weight percentile and rate of LGA neonates were significantly higher in pregnancies in which the ΔCRL was ½ week or greater (P = .007 and .033, respectively). There was a significant linear correlation between the ΔCRL and birth weight percentile (P = .001). On multivariate logistic regression analysis, the ΔCRL was the only significant predictor of an LGA neonate (odds ratio, 1.6; 95% confidence interval, 1.07–2.4; P = .023). Conclusions. Pregnancies with LGA neonates are characterized by larger‐than‐expected CRL measurements at 11 to 14 weeks' gestation.     

New Regression Formulas for Sonographic Weight Estimation Within 10, 7, and 3 Days of Delivery

Objectives. The purpose of this study was to develop new regression formulas based on large numbers of sonographic examinations performed within 10, 7, and 3 days of delivery. Methods. Sonographic fetal biometric measurements and delivery ward data for an unselected population were analyzed. Multivariate linear regression models were fitted to the sonographic data to predict the actual birth weight (BW) within 10, 7, and 3 days. Results. The analyses included 6289, 5449, and 4007 patients who underwent sonographic examinations within 10, 7, and 3 days of delivery, respectively. All models yielded very high correlation coefficients (r = 0.927–0.958; R² = 0.859–0.918), low mean deviations between the calculated and actual BWs (6.4%–6.6% ± 1 SD of 5.5%–5.9%), and high percentages of the calculated BW within 10% of the actual BW (78.5%–80.4%). Estimated fetal weight analyses made within 3 days of delivery yielded slightly better results than within 7 and 10 days. Conclusions. The new regression formulas yielded overall similar results, with a small advantage for estimates calculated within 3 days of delivery. Further prospective studies are needed to compare the accuracy of these formulas with those used to date.     

Prenatal Sonographic Diagnosis of Intrahepatic Portosystemic Shunts

The incidence of fetal portosystemic anastomoses is unknown, and it is presumed that many cases remain undetected, as visualization of the hepatic vasculature is not part of the routine 20‐week sonographic scan in pregnancy. However, portosystemic anastomoses are associated with fetal growth restriction due to a diminished oxygen supply to hepatocytes and, hence, downregulation of liver function. In these cases, uteroplacental perfusion might be normal.     

Umbilical Artery Doppler Indices in Small for Gestational Age Fetuses

Objective. The purpose of this study was to compare the screening efficiency of the umbilical artery systolic to diastolic ratio (S/D), pulsatility index (PI), and absent end-diastolic flow (AEDF) for adverse pregnancy outcomes and placental abnormalities in small for gestational age (SGA) fetuses. Methods. We conducted a retrospective cohort study of Doppler examinations of 161 nonanomalous SGA fetuses. The reliability of the S/D and PI were quantified by intraclass correlation coefficients. The association of the S/D, PI, and AEDF with adverse outcomes and placental abnormalities was compared by the χ² test. Results. There was a simple association of Doppler results with adverse outcomes, which was mitigated when controlled for gestational age. For all measures of adverse outcomes, the specificity of abnormal Doppler results exceeded the sensitivity, and the negative predictive value was greater than the positive predictive value. Comparing the S/D with the PI, there was no significant difference in the sensitivity; however, the specificity of the PI was at least 90% and exceeded that of the S/D for all outcomes. The intraclass correlation coefficients of the S/D and PI were similar, indicating no difference in reliability. Placental abnormalities were significantly more common in cases with abnormal Doppler values (positive predictive value, 94%) with no overlap in the types of placental lesions in most cases. Conclusions. As an initial screen for adverse outcomes in SGA fetuses, the umbilical artery Doppler S/D, PI, and AEDF were imprecise. However, these measures were all strongly and similarly predictive of placental abnormalities, especially lesions of maternal underperfusion and fetal vascular obstruction.