Objective: Assess the relationship of time to first expression after very preterm birth and mothers' own milk quantity.
Design: A cohort study (nested within a randomised trial).
Setting: Four neonatal units in the UK.
Patients: 132 mothers of single or twin infants born at 23+0 to 31+6 weeks postmenstrual age.
Exposures: Time to the first attempt to express after birth.
Primary outcomes: 24-hour mother's own milk yield on days 4, 14 and 21 after birth.
Results: Median time to first expression attempt was 6 hours. 51.7% expressed within 6 hours of birth (62/120) and 48.3% expressed more than 6 hours after birth (58/120). Expressing within 6 hours of birth was associated with higher milk yield on day 4 (88.3 g, 95% CI 7.1 to 169.4) and day 14 (155.7 g, 95% CI 12.2 to 299.3) but not on day 21 (73.6 g, 95% CI -91.4 to 238.7). There was an interaction between expressing frequency and time to first expression (p<0.005), with increased expressing frequency being associated with higher yield only in those who expressed within 6 hours. Expressing within 2 hours of birth was not associated with further milk yield increase.
Conclusions: Mothers who expressed within 6 hours of birth had higher milk yield, and a greater yield per expressing session, in the first 3 weeks after birth. This information will be highly motivating for families and the clinicians supporting them. There was no evidence of further benefit of extremely early expression (first 2 hours after birth).
Trial registration number: ISRCTN 16356650.
Keywords: Intensive Care Units, Neonatal; Neonatology.
© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY. Published by BMJ.