Fetal thoracic circumference in mid‐pregnancy and infant lung function

BACKGROUND AND AIM: Impaired lung function in early infancy is associated with later wheeze and asthma, while fetal thoracic circumference (TC) predicts severity of neonatal lung hypoplasia. Exploring fetal origins of lung function in infancy, we aimed to determine if fetal TC in mid‐pregnancy was associated with infant lung function. METHODS: From the prospective Scandinavian general population‐based PreventADALL mother–child birth cohort, all 851 3‐month‐old infants with tidal flow‐volume measurements in the awake state and ultrasound fetal size measures at 18 (min–max 16–22) weeks gestational age were included. Associations between fetal TC and time to peak tidal expiratory flow to expiratory time (t (PTEF)/t (E)) were analyzed in linear regression models. To account for gestational age variation, we adjusted TC for simultaneously measured general fetal size, by head circumference (TC/HC), abdominal circumference (TC/AC), and femur length (TC/FL). Multivariable models were adjusted for maternal age, maternal asthma, pre‐pregnancy body mass index, parity, nicotine exposure in utero, and infant sex. RESULTS: The infants (47.8% girls) were born at mean (SD) gestational age of 40.2 (1.30) weeks. The mean (SD) t (PTEF)/t (E) was 0.39 (0.08). The mean (SD) TC/HC was 0.75 (0.04), TC/AC 0.87 (0.04), and TC/FL 4.17 (0.26), respectively. Neither TC/HC nor TC/AC were associated with infant t (PTEF)/t (E) while a week inverse association was observed between TC/FL and t (PTEF)/t (E) ([Formula: see text] = −0.03, 95% confidence interval [−0.05, −0.007], p = 0.01). CONCLUSION: Mid‐pregnancy fetal TC adjusted for fetal head or abdominal size was not associated with t (PTEF)/t (E) in healthy, awake 3‐month‐old infants, while a weak association was observed adjusting for fetal femur length.