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

Publication Type
Journal Article
Year of Publication
Amyx, Melissa M; Albert, Paul S; Bever, Alaina M; Hinkle, Stefanie N; Owen, John; Grobman, William A; Newman, Roger B; Chien, Edward K; Gore-Langton, Robert E; Buck Louis, Germaine M; Grantz, Katherine L
Paediatr Perinat Epidemiol
Date Published
2019 09
Adult; Diseases in Twins; Female; Fetal Development; Fetal Growth Retardation; Fetal Weight; Gestational Age; Humans; National Institute of Child Health and Human Development (U.S.); Predictive Value of Tests; Pregnancy; Pregnancy, Twin; Prenatal Care; Twins, Dizygotic; Ultrasonography, Prenatal; United States

BACKGROUND: Birthweight discordance is well studied, with less known about longitudinal inter-twin differences in foetal growth.

OBJECTIVE: To examine inter-twin per cent differences in EFW (EFW ), head (HC ) and abdominal circumference (AC ), and femur length (FL ) across gestation in dichorionic twin gestations and explore associated characteristics.

METHODS: Foetal biometrics were assessed by ultrasound and EFW calculated at ≤6 study visits among women with dichorionic twin pregnancies enrolled in the NICHD Fetal Growth Studies cohort (US, 2012-2013). Inter-twin per cent difference was defined: ([Size  - Size ]/Size  × 100). Linear mixed models evaluated per cent differences in foetal biometrics at 15 weeks and their change per week overall and by maternal/neonatal characteristics in unadjusted and adjusted models.

RESULTS: In 140 pregnancies, inter-twin per cent differences increased across gestation for EFW (0.18%/week, 95% confidence interval [CI] 0.10, 0.27), HC (0.03%/week, 95% CI 0.00, 0.06), and AC (0.03%/week, 95%CI -0.01, 0.08) but decreased for FL (-0.03%/week, 95% CI -0.09, 0.02). After adjustment, change in EFW difference across gestation differed by pre-pregnancy body mass index (BMI [kg/m ]; underweight [<18.5]; normal weight [18.5-24.9]; overweight [25.0-29.9]; obese [≥30.0]; P  = .022); and conception method (in vitro fertilisation [IVF], intrauterine insemination, ovulation induction medication, donor egg/embryo, none; P  = .060). While EFW difference increased with normal pre-pregnancy BMI (0.24%/week, 95% CI 0.12, 0.37), little change was noted with pre-pregnancy obesity (0.01%/week, 95% CI -0.15, 0.17). EFW difference increased in conceptions without fertility treatments (0.23%/week, 95% CI 0.11, 0.34) but not IVF conceptions (-0.00%/week, 95% CI -0.16, 0.16). Similar patterns of differences across gestation were noted for HC by conception method (P  = .026) and AC by pre-pregnancy BMI (P  = .071); changes in HC differed by parity (nulliparous, multiparous; P  = .004).

CONCLUSIONS: EFW difference increased across gestation in dichorionic twins, but remained stable with pre-pregnancy obesity or IVF conception, patterns mirrored for HC and AC. Research is needed to understand pathologic versus physiologic differential twin growth trajectories.