Estimation of fetal weight by ultrasound prior to 33 weeks gestation

Ultrasonographic estimation of fetal weight: development of new model and assessment of performance of previous models

OBJECTIVES

To develop a new formula for ultrasonographic estimation of fetal weight and evaluate the accuracy of this and all previous formulae in the prediction of birth weight.

METHODS

The study population consisted of 5163 singleton pregnancies with fetal biometry at 22-43 weeks' gestation and live birth of a phenotypically normal neonate within 2 days of the ultrasound examination. Multivariable fractional polynomial analysis was used to determine the combination of variables that provided the best-fitting models for estimated fetal weight (EFW). A systematic review was also carried out of articles reporting formulae for EFW and comparing EFW to actual birth weight. The accuracy of each model for EFW was assessed by comparing mean percentage error, absolute mean error (AE), proportion of pregnancies with AE ≤ 10% and Euclidean distance.

RESULTS

The most accurate models, with the lowest Euclidean distance and highest proportion of AE ≤ 10%, were provided by the formulae incorporating ≥ 3 rather than < 3 biometrical measurements. The systematic review identified 45 studies describing a total of 70 models for EFW by various combinations of measurements of fetal head circumference (HC), biparietal diameter, femur length (FL) and abdominal circumference (AC). The most accurate model with the lowest Euclidean distance and highest proportion of AE ≤ 10% was provided by the formula of Hadlock et al., published in 1985, which incorporated measurements of HC, AC and FL; there was a highly significant linear association between EFW and birth weight (r = 0.959; P < 0.0001), and EFW was within 10% of birth weight in 80% of cases. The performance of the best model developed in this study, utilizing HC, AC and FL, was very similar to that of Hadlock et al. CONCLUSION: Despite many efforts to develop new models for EFW, the one reported in 1985 by Hadlock et al., from measurements of HC, AC and FL, provides the most accurate prediction of birth weight and can be used for assessment of all babies, including those suspected to be either small or large. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Association of third-trimester abdominal circumference with provider-initiated preterm delivery

OBJECTIVE

Evaluate the association of a small third-trimester abdominal circumference (AC < 10th percentile) in the setting of a normal estimated fetal weight (EFW ≥ 10th percentile) with gestational age at delivery, indication for delivery and neonatal outcomes.

METHODS

Retrospective cohort study at an academic hospital of women with singleton pregnancy seen for ultrasound from 28+0-33+6 weeks of gestation during 2009-2011. Outcomes were compared between two groups: normal AC (AC and EFW ≥ 10th percentile) and small AC (AC < 10th percentile and EFW ≥ 10th percentile).

RESULTS

Among 592 pregnancies, fetuses in the small AC group (n = 55) experienced a higher incidence of overall preterm delivery (RR: 2.2, 95% CI: 1.3-3.7) and provider-initiated preterm delivery (RR: 3.7, CI: 1.8-7.5) compared to those in the normal AC group (n = 537). Neonates in the small AC group had a lower median birth weight whether delivered at term (p < 0.001) or preterm (p = 0.04), but were not more likely to experience intensive care unit admission or respiratory distress syndrome (all p ≥ 0.35).

CONCLUSIONS

Small AC, even in the setting of an EFW ≥ 10th percentile, was associated with a higher incidence of overall and provider-initiated preterm delivery despite similar neonatal outcomes. Further investigation is warranted to determine whether these preterm deliveries could be prevented.

Prediction of newborn birth weight based on the estimation at 20-24 weeks of gestation

OBJECTIVE

The aim of this study was to develop a mathematical equation to predict the birth weight during the second trimester at 20-24 weeks of gestation.

MATERIALS AND METHODS

In a university hospital, 110 healthy pregnant women were eligible for inclusion at 20-24 weeks of gestation. We recorded the maternal weight (pre-pregnancy, mid-pregnancy, and at delivery) and body mass index (BMI), newborn birth weight, time period from ultrasound examination to term delivery, and also the fetal biometrics sonographically at 20-24 weeks of gestation. Pearson's correlation was used to verify the extent of the relationship between all the above measurements and the newborn birth weight. Multiple regressions with the stepwise method were used to analyze maternal weight factors, fetal biometrical factors, and pregnancy interval. An equation for term birth weight estimation during the second trimester was determined.

RESULTS

Maternal BMI at mid-pregnancy, time interval from mid-pregnancy to term, and abdominal circumference had the highest correlation with newborn birth weight (r = 0.388, 0.341, and 0.315, respectively, p < 0.05). Using the stepwise regression analysis, an optimal formula with variance of 0.303 was derived: estimated birth weight = -700 + 49.766 × (mid-pregnancy BMI [kg/m2]) + 13.362 × (time interval from mid-pregnancy to term delivery [days]) + 68.696 × (abdominal circumference [cm]).

CONCLUSION

We propose an accurate, simple, and easy formula to better assess the newborn birth weight at mid-pregnancy for the Asian population. Mid-pregnancy BMI was a more significant factor for birth weight estimation than other maternal weight factors in this study.

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; R(2) = 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.