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

Melissa M. Amyx, Paul S. Albert, Alaina M. Bever, Stefanie N. Hinkle, John Owen, William A. Grobman, Roger B. Newman, Edward K. Chien, Robert E. Gore-Langton, Germaine M. Buck Louis, Katherine L. Grantz*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


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: ([Sizelarger twin − Sizesmaller twin]/Sizelarger twin × 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/m2]; underweight ['18.5]; normal weight [18.5-24.9]; overweight [25.0-29.9]; obese [≥30.0]; Pinteraction =.022); and conception method (in vitro fertilisation [IVF], intrauterine insemination, ovulation induction medication, donor egg/embryo, none; Pinteraction =.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 (Pinteraction =.026) and AC% by pre-pregnancy BMI (Pinteraction =.071); changes in HC% differed by parity (nulliparous, multiparous; Pinteraction =.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.

Original languageEnglish (US)
Pages (from-to)332-342
Number of pages11
JournalPaediatric and Perinatal Epidemiology
Issue number5
StatePublished - Sep 1 2019


  • dichorionic
  • estimated foetal weight
  • foetal growth
  • twin
  • twin discordance

ASJC Scopus subject areas

  • Epidemiology
  • Pediatrics, Perinatology, and Child Health


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