Authors
Newell, S 1,2, Prajapati, C 3, Smith-Collins, A 1,2, Burden, C 2,3, Lenguerrand, E 2, Luyt, K 1,2, Denbow, M 1,2

Institution(s)
1. University Hospitals Bristol NHS Foundation Trust, Bristol
2. University of Bristol
3. North Bristol NHS Trust

Introduction
Discordant birthweight in twins has been associated with poorer neurological outcomes. However, the cause of underlying neuromorbidity in growth discordant twins is unknown (1,2). Studies looking at head size in infancy showed that a smaller head circumference is associated with poorer neurological outcomes. Therefore, the aim of this study was to assess the association between birthweight discordance and brain volume.

Methods
This was a multicentre prospective cohort study over a two-year period. Participants underwent a neonatal MRI scan at term corrected gestational age. A 3T scanner was used to acquire T1 weighed scan images, which were processed and volumetric data extracted. Outcome measures were: absolute brain volume (cm3) and relative intertwin brain volume discordance (%). Regression analyses were performed to assess the relationship between outcome measures and relative intertwin birthweight discordance (%).

Results
After adjusting for various confounders (including gestational age, birthweight and gender), there was strong evidence that increased birthweight discordance was associated with a reduction in absolute brain volume in: monochorionic twins (p 0.007), gender concordant dichorionic twins (p <0.001) and gender discordant dichorionic twins (p 0.010).
There was also strong evidence that increased birthweight discordance was associated with increased brain volume discordance in: monochorionic twins (p 0.028), gender concordant dichorionic twins (p 0.002) and gender discordant twins (p 0.020).

Conclusions
This is the first study to investigate the association of birthweight discordance with brain volume in twins. Our findings indicate that an increase in birthweight discordance is associated with a reduction in brain tissue volume and an increase in intertwin relative brain volume discordance.

References: 1. Adegbite, A. et al. Neuromorbidity in preterm twins in relation to chorionicity and discordant birth weight. AJOG (2004). 2.
Harper, L. M. et al. Significance of growth discordance in appropriately grown twins. AJOG (2013)