Objective: Fetal malnutrition can negatively affect lung development, leading to increased respiratory morbidity and reduced lung function later in life. Yet, studies regarding the impact of fetal growth restriction (FGR) on lung function in singletons may be influenced by genetic, obstetric, and maternal factors. Therefore, we aim to investigate childhood lung function in monochorionic (MC) twins with selective FGR (sFGR) eliminating these confounding factors.

Methods: Spirometry was performed in MC twins with sFGR, defined as birth weight discordance ?20%, born in our center between 2002-2017. Outcome measures consisted of forced expiratory volume in one second (FEV1), forced vital capacity (FVC), residual volume (RV), total lung capacity (TLC), and transfer factor for carbon monoxide (TLCO). Outcomes were compared between smaller and larger twins.

Preliminary results: We included 43 twin pairs with sFGR born at a median gestational age of 34.6 (interquartile range (IQR) 32.6-36.0) weeks with median birthweights of 1489 (IQR 1166-1869) grams for smaller twins and 2113 (IQR 1690-2710) grams for larger twins. Spirometry was of sufficient quality in 32 twin pairs, with a median age of 11 years (8-13). Smaller twins had significantly lower z-scores for FEV1, FVC, TLC and TLCO compared to larger twins. FEV1%FVC and RV%TLC did not significantly differ.

Conclusions: Although being genetically identical, sFGR is associated with a reduction in static lung volume with an equivalent decrease in dynamic lung function, suggesting that adverse growth conditions in utero negatively affect lung development and function. This can contribute to an increase in respiratory morbidities later in life.