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Introduction: Mothers at risk of preterm birth are treated with antenatal corticosteroids, which have advantageous effects for prematurely born infants. Accelerated villous maturation in the placenta is also associated with improved perinatal outcome. The primary aim of this study was to examine the association between antenatal corticosteroids and accelerated villous maturation. The secondary aim was to study associations with other placental pathologies.

Material and methods: A retrospective cohort study including 105 women who had (n = 75) or had not (n = 30) been treated with antenatal corticosteroids. The women gave birth between 22+0 and 26+6 weeks of gestation in Stockholm County between 1 April 2004 and 31 March 2007. A pathologist blinded to all clinical data except gestational age examined the placental slides to identify pathology parameters. The outcomes were correlated with antenatal corticosteroid treatment, and confounding factors were adjusted using logistic regression.

Results: Accelerated villous maturation was significantly higher in the group treated with corticosteroids (odds ratio 16, 95% CI 2.4–690, p = 0.0005). After adjustment for gestational age and preeclampsia, the difference remained significant (odds ratio 8.9, 95% CI 1.2–389, p = 0.021). No significant associations were found regarding the secondary outcome variables, after adjusting for possible confounders.

Conclusions: Antenatal corticosteroid treatment before preterm birth is associated with accelerated villous maturation. This could be one of the pathways by which corticosteroids are beneficial for preterm infants.