Associations between estimated foetal weight discordance and clinical characteristics within dichorionic twins: The NICHD Fetal Growth Studies

Patterns of discordant growth and adverse neonatal outcomes in twins

BACKGROUND

Intertwin size discordance is an independent risk factor for adverse neonatal outcomes in twin pregnancies. However, size discordance at a given point in gestation fails to take into consideration information, such as the timing of onset and the rate of progression of discordance, that may be of prognostic value.

OBJECTIVE

In this study, we aimed to identify distinct patterns of discordant fetal growth in twin pregnancies and to determine whether these patterns are predictive of adverse pregnancy outcomes.

STUDY DESIGN

This was a retrospective cohort study of women with twin pregnancies in a single tertiary referral center between January 2011 and April 2020, who had at least 3 ultrasound examinations during pregnancy that included assessment of fetal biometry. Size discordance was calculated at each ultrasound examination, and pregnancies were classified into 1 of 4 predetermined patterns based on the timing of onset and the progression of discordance: pattern 1, no significant discordance group (referent); pattern 2, early (<24 weeks' gestation) progressive discordance group; pattern 3, early discordance with plateau group; or pattern 4, late (≥24 weeks' gestation) discordance group. The associations of discordance pattern (using pattern 1 as referent) with preterm birth, preeclampsia, size discordance at birth, and birthweight<10th percentile were expressed as adjusted relative risk with 95% confidence intervals and were compared with those observed for a single measurement of size discordance at 32 weeks' gestation.

RESULTS

Of 2075 women with a twin gestation who were identified during the study period, 1059 met the study criteria. Of the 1059 women, 599 (57%) were classified as no significant discordance (pattern 1), 23 (2%) as early progressive discordance (pattern 2), 160 (15%) as early discordance with plateau (pattern 3), and 277 (26%) as late discordance (pattern 4). The associations of discordance pattern with preterm birth at <34 weeks' gestation and preeclampsia were strongest for pattern 2 (rates of 43% [adjusted relative risk, 3.43; 95% confidence interval, 2.10-5.62] and 17% [adjusted relative risk, 5.81; 95% confidence interval, 2.31-14.60], respectively), intermediate for pattern 3 (rates of 23% [adjusted relative risk, 1.82; 95% confidence interval, 1.28-2.59] and 6% [adjusted relative risk, 2.08; 95% confidence interval, 1.01-4.43], respectively), and weakest for pattern 4 (rates of 12% [adjusted relative risk, 0.96; 95% confidence interval, 0.65-1.42] and 4% [adjusted relative risk, 1.41; 0.68-2.92], respectively). In contrast, a single measurement of size discordance at 32 weeks' gestation showed no association with preeclampsia and only a weak association with preterm birth at <34 weeks' gestation.

CONCLUSION

We identified 4 distinct discordance growth patterns among twins that demonstrated a dose-response relationship with adverse outcomes and seemed to be more informative than a single measurement of size discordance.

Ultrasound in the prediction of birthweight discordance in dichorionic twins

INTRODUCTION

Large birthweight discrepancy has been identified as a risk factor for perinatal morbidity and mortality in twin pregnancies. However, it remains unclear whether such discordance can be predicted by various biological indices with specific cut-off values, and how these depend on the gestational age. We aimed to determine the most effective way to predict large birthweight discordance at various gestational ages.

MATERIAL AND METHODS

A retrospective cohort study of dichorionic twins, live-born between 2008 and 2018, was conducted. Discordances in biparietal diameter, head circumference, humerus and femur length, abdominal circumference, and estimated fetal weight were calculated-([larger twin - smaller twin] / larger twin) × 100%-and compared between those with and without a large birthweight discordance (≥20%). Receiver operating characteristic curves were constructed to analyze the predictive characteristics of each parameter.

RESULTS

Of 598 dichorionic twin pregnancies included, 83 (13.9%) had a birthweight discordance ≥20%. Group differences in biparietal diameter and head circumference discordance were the earliest to emerge (before 20 weeks of gestation), but became insignificant after 36 weeks, followed by humerus and femur length, estimated fetal weight discordance (after 20 weeks), and abdominal circumference discordance (after 28 weeks). The best predictors (with cut-off values) were discordance in biparietal diameter ≥7.8% at <20 weeks, head circumference ≥4.5% at 20-23⁺⁶  weeks, humerus length ≥4.5% at 24-27⁺⁶  weeks, and estimated fetal weight discordance (≥11.6% at 28-31⁺⁶  weeks, ≥10.5% at 32-35⁺⁶  weeks, and ≥15.0% ≥36 weeks), with sensitivity and specificity of 52%-77% and 69%-82%, respectively.

CONCLUSIONS

Different predictors and cut-off values may be useful for predicting large inter-twin birthweight discordance in dichorionic twins at different gestational ages. It is more accurate to use biparietal diameter and head circumference discordance in the early second trimester, humerus length discordance in the late second trimester, and estimated fetal weight discordance in the third trimester.