Description of probiotic use in preterm infants in England and Wales 2016-2022.

Objective: To describe the use of probiotics among preterm infants in neonatal units and explore factors that influence exposure.

Design: Observational study using prospectively recorded health data.

Setting: England and Wales.

Patients: 48 048 infants born at <32 weeks gestational age (GA) and admitted to a neonatal unit between 1 January 2016 and 31 December 2022.

Main outcome measures: Measures of probiotic use (number and proportion of infants exposed to probiotics, postnatal age of first probiotic exposure and discontinuation).

Results: The proportion of infants who received probiotics increased from 9% to 54% over the study period. Median GA of infants given probiotics was 29⁺³ weeks (IQR 27⁺³-30⁺⁶). Probiotics were started on median day 5 (IQR 2-8), earlier for those born at >28 weeks GA (median day 4, IQR 2-7), most frequently after enteral feeds (66% of exposed infants) and were usually discontinued between 32 and 36 weeks postmenstrual age (PMA) (47% at 32⁺⁰-33⁺⁶ weeks PMA, 33% at 34⁺⁰-35⁺⁶ weeks PMA). Among infants cared for in probiotic neonatal intensive care units (defined as units where 50% or more infants born <32 weeks gestation were exposed to probiotics), 23% were never given probiotics. Infants from whom probiotics were withheld had a lower gestational age, lower birth weight z score and higher illness severity score or were more mature.

Conclusions: By 2022, over half of infants born at <32 weeks GA were exposed to probiotics, but almost one quarter did not receive them despite being in a probiotic unit. Our findings help inform the interpretation of observational data and the design of future studies addressing the continued uncertainty around the safety and efficacy of probiotics.