Patterns of Second- and Third-Trimester Growth and Discordance in Twin Pregnancy: Analysis of the Southwest Thames Obstetric Research Collaborative (STORK) Multiple Pregnancy Cohort

Abstract

Introduction: This study investigates patterns of intertwin size discordance in dichorionic diamniotic (DCDA) and monochorionic diamniotic (MCDA) twin pregnancies. Material and Methods: Ultrasound measurements of twin pregnancies, from 14 weeks to term, were collected by 9 hospitals over a 10-year period. This analysis considers the modelled and observed levels of discordance in abdominal circumference (AC) and estimated fetal weight (EFW) in relation to gestational age. Fitted models were analysed to produce charts displaying the expected range of intertwin discordance in AC and EFW at any given examination. Results: The dataset for analysis included a total of 9,866 ultrasound examinations in 1,802 DCDA and 323 MCDA twin pregnancies. The 95th percentile of intertwin discordance in EFW increased from 18.3% (95% CI, 17.8-18.7%) at 20 weeks to 21.9% (95% CI, 21.3-22.4%) at 30 weeks for DCDA pregnancies. The 95th percentile for intertwin discordance in AC was stable at 10-11% for this period. Slightly higher levels of discordance were observed for MCDA than for DCDA pregnancies. Discussion: The expected range of intertwin discordance in EFW and AC shows differences with gestational age and between DCDA and MCDA pregnancies.

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

“…A contemporary longitudinal study estimating percentiles of EFW % difference across gestation supports our finding that EFW % differences increase with gestation, 22 though an older, smaller study found little change in percentiles of EFW % difference across F I G U R E 1 Per cent difference in EFW across gestation by subgroups of significant interaction terms (N = 140; NICHD Fetal Growth Studies-Dichorionic Twins, United States, 2012-2013). Significance of interaction term determined using global F test (ie slope of per cent difference in EFW across gestation) by characteristics of interest (BMI: P = .021; fertility treatment type: P = .049).…”

“…A contemporary longitudinal study estimating percentiles of EFW % difference across gestation supports our finding that EFW % differences increase with gestation, though an older, smaller study found little change in percentiles of EFW % difference across gestation . In addition, our finding that EFW % difference increased across gestation within low‐risk subgroups suggests that modest increases across gestation (provided EFW % difference remains low [~10%]) may be physiologic.…”

“…study also found increases in per cent differences in abdominal circumference starting around 16 weeks' gestation 22. Additional research to examine the relationships between changes in EFW % difference and in other biometric measures across gestation and adverse neonatal outcomes is needed to better distinguish normal physiologic from pathologic changes in inter-twin differences in foetal biometrics.Comparing our pre-pregnancy BMI findings to studies of birthweight discordance, an earlier study found no difference in birthweight discordance by BMI 30.…”

“…In addition, our finding that EFW % difference increased across gestation within low‐risk subgroups suggests that modest increases across gestation (provided EFW % difference remains low [~10%]) may be physiologic. Longitudinal per cent differences in other foetal biometric measures across gestation are less well characterised, though the same contemporary longitudinal study also found increases in per cent differences in abdominal circumference starting around 16 weeks' gestation . Additional research to examine the relationships between changes in EFW % difference and in other biometric measures across gestation and adverse neonatal outcomes is needed to better distinguish normal physiologic from pathologic changes in inter‐twin differences in foetal biometrics.…”

Gender-Specific Antenatal Growth Reference Charts in Monochorionic Twins

“…The significant independent effect of chorionicity on birthweight suggests that MC placentation in itself has an effect on intrauterine growth and discordance [9, 10]. On the other hand, sex differences in fetal growth have already been established and it is known that male fetuses have a higher growth rate compared to females in singletons [11].…”