Objectives

Fetal growth restriction (FGR) may permanently alter brain development resulting in lifelong structural and functional changes. However, in studies addressing this research question, FGR singletons are primarily compared to matched appropriately-grown singletons, a design which is inherently biased by differences in genetic and maternal factors. To overcome these limitations, we conducted a within-pair comparison of structural cerebral measurements in identical twin pairs discordant for fetal growth.

Methods

Structural cerebral measurements on neonatal cerebral ultrasound were compared between the smaller twin and larger twin of monochorionic twins with selective fetal growth restriction (sFGR), defined as a birth weight discordance ≥ 20%, born in our center between 2010-2020. Each twin pair was also matched to an appropriately-grown singleton based on sex and gestational age at birth.

Results

We included 58 twin pairs with sFGR, with a median gestational age at birth of 31.7 (IQR 29.9-33.8) weeks and a median birth weight for the smaller twin and the larger twin of respectively 1155 grams versus 1725 grams (median birth weight discordance of 32%). The smaller twin had significantly smaller cerebral structures (corpus callosum, vermis, cerebellum), white/deep gray matter and intracranial surface and volume. Intracranial volume discordance and birth weight discordance correlated significantly (r = 0.443, p = 0.004). Intracranial volume discordance was smaller as opposed to birth weight discordance (19% vs. 32% respectively, p < 0.0001). After correction for intracranial volume, all observed differences (except for biparietal diameter) ceased to exist.

Conclusions

sFGR in monochorionic twins is associated with an overall, proportional restriction in brain growth on neonatal cerebral ultrasound for the smaller twin, in line with previous singleton studies. The amount of birth weight discordance translates into a discordance in the size of brain structures as well, albeit smaller as opposed to the amount of birth weight discordance.

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