First-trimester inter- and intrafetal size discrepancies in bichorionic twins conceived by in vitro fertilization: can it predict pregnancy outcome?

OBJECTIVE: To evaluate the association between first-trimester inter- and intrafetal size discrepancies and pregnancy outcome, among bichorionic-biamniotic twins conceived by IVF.

DESIGN: A retrospective study design was used.

SETTING: Tertiary university-affiliated medical center.

PATIENT(S): All women with a viable first-trimester bichorionic-biamniotic twin gestation, who conceived after IVF in 2007-2015.

INTERVENTION(S): None.

MAIN OUTCOME MEASURE(S): The association between fetal size differences and pregnancy outcome was analyzed. Intrafetal size discordance was defined as a difference between the actual gestational age calculated by ovum pickup (OPU) date and the evaluated gestational age by crown-rump length (CRL), for each twin. Intertwin size discrepancy was defined as a difference in CRL between the twins. The primary outcome was the number of live-born fetuses; the secondary outcome measures were gestational age at birth, birth weight percentile, and birth weight discordancy.

RESULT(S): A total of 277 women met the study criteria and were divided into three groups by outcome: 218 (78.7%) live-born twins, 41 (14.8%) live-born singleton, and 19 (6.5%) non-live-born pregnancy. Among the smaller than expected twin, the association of CRL-OPU differences with the primary outcome was significant for twin live-born delivery (-1.43 day), singleton live-born delivery (-4.12 days), and non-live-born pregnancy (-6.72 days). For the relatively larger twin, the association was significant for non-live-born pregnancy (-4.33 days) compared with any live-born delivery, either singleton (-0.95 days) or twin (-0.21 days).

CONCLUSION(S): Among IVF conceived twin gestations, a CRL-OPU gap was associated with an increased risk of a negative pregnancy outcome.