Objective To compare short-term outcomes after placental transfusion (delayed cord clamping (DCC) or umbilical cord milking (UCM)) versus immediate cord clamping among extremely preterm infants.

Design Retrospective study.

Setting The Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network registry.

Patients Infants born <29 weeks’ gestation in 2016 or 2017 without congenital anomalies who received active treatment after delivery.

Intervention/exposure DCC or UCM.

Main outcome measures Primary outcomes: (1) composite of mortality or major morbidity by 36 weeks’ postmenstrual age (PMA); (2) mortality by 36 weeks PMA and (3) composite of major morbidities by 36 weeks’ PMA. Secondary composite outcomes: (1) any grade intraventricular haemorrhage or mortality by 36 weeks’ PMA and (2) hypotension treatment in the first 24 postnatal hours or mortality in the first 12 postnatal hours. Outcomes were assessed using multivariable regression, adjusting for mortality risk factors identified a priori, significant confounders and centre as a random effect.

Results Among 3116 infants, 40% were exposed to placental transfusion, which was not associated with the primary composite outcome of mortality or major morbidity by 36 weeks’ PMA (adjusted OR (aOR) 1.26, 95% CI 0.95 to 1.66). However, exposure was associated with decreased mortality by 36 weeks’ PMA (aOR 0.71, 95% CI 0.55 to 0.92) and decreased hypotension treatment in first 24 postnatal hours (aOR 0.66, 95% CI 0.53 to 0.82).

Conclusion In this extremely preterm infant cohort, exposure to placental transfusion was not associated with the composite outcome of mortality or major morbidity, though there was a reduction in mortality by 36 weeks’ PMA.

Trial registration number NCT00063063.