If you are among the 500,000 mothers who give birth prematurely each year, your answer to the question, “Got milk?” may be, “Not yet.” A group of Australian researchers recently investigated the effect of preterm birth and antenatal corticosteroids (steroids given prior to birth) on the timing of lactogenesis II—the onset of copious milk secretion which usually occurs within 2 days of birth (mothers describe it as the period when their “milk comes in.”)

Fifty women who had received betamethasone (a corticosteroid) prior to birth and were expressing milk for a preterm infant less than 34 weeks gestation were included in the study. The average gestational age at the time of delivery was 31 weeks (range 24.2-33.7).

The volume of milk expressed in 24-hour periods was measured on postpartum days 1 to 10. Milk volume was positively associated with gestational age—the higher the gestational age the higher the milk yield. Gestational age, reportedly, modified the effect of interval between betamethasone administration and birth on milk volume. Women who gave birth at 28 to 34 weeks and 0 to 2 days after betamethasone treatment expressed significantly larger volumes of milk compared to women who gave birth at 28 to 34 weeks and 3 to 9 days after steroid treatment. Delayed lactogenesis II was not seen in women who gave birth more than 10 days after betamethasone treatment suggesting that betamethasone-induced changes in lactation resolved with time and that when birth was more than 10 days after treatment, lactogenesis II was not affected.

The findings suggest that antenatal corticosteroids may delay the onset of lactogenesis II depending on gestational age at the time of birth and the time interval between corticosteroid treatment and birth.

Given the significant advantages of mothers’ own milk for the growth and development of preterm babies, more research is need on the effects of single and multiple courses of antenatal corticosteroids and preterm birth on lactation outcomes. Because low milk production in the first week postpartum has implications for breastfeeding duration, the need for additional lactation support in mothers who give birth prematurely must be recognized.