Children exposed in the womb to antenatal corticosteroids before 34 weeks of pregnancy had a small increased risk of childhood cancer, according to a large population-based study presented recently at the SMFM 2026 Pregnancy Meeting .
This study also has implications for families facing fetal and neonatal alloimmune thrombocytopenia (FNAIT), a rare condition often treated with corticosteroids.
While the overall cancer risk for these patients remained low, researchers found a modest but statistically significant association after adjusting for key factors.
Antenatal corticosteroids, often called ACS, are routinely given to pregnant women at risk of preterm delivery. The medication helps speed up fetal lung development and reduces serious newborn complications. In high-risk pregnancies, including some affected by FNAIT where early delivery may be necessary to prevent bleeding complications, these steroids can be lifesaving.
The study followed 196,377 singleton live births at a single tertiary medical center between 1991 and 2021. Of these, 3,634 infants, or 1.9%, were exposed to ACS before 34 weeks of gestation. The remaining 192,743 were not exposed. Mothers who received ACS were slightly older on average, 28.9 vs 28.1 years, and delivered earlier, at a mean of 36.1 weeks compared with 39.0 weeks. Preterm birth occurred in 42.40% of the exposed group and 6.30% of the unexposed group.
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Childhood cancer was diagnosed in 9 children in the exposed group, or 0.25%, and in 438 children in the unexposed group, or 0.23%, a difference that was not statistically significant in simple comparisons. Rates of leukemia, lymphoma and central nervous system tumors were similar between groups. Endocrine cancers were rare but occurred more often in exposed children, with an odds ratio of 4.42.
“While ACS remains essential in managing threatened preterm birth, this association may partly reflect indication bias, as more vulnerable fetuses are more likely to receive treatment,” noted the authors of this study.
When researchers used a Cox proportional hazards model adjusting for gestational age and ethnicity, ACS exposure was linked to a 42% increased risk of childhood malignancy, with an adjusted hazard ratio of 1.42 and a 95% confidence interval of 1.01 to 1.98. Preterm birth itself was not independently associated with cancer risk.
For patients and families, including those managing FNAIT, the findings may sound concerning but should be viewed in context. The absolute risk of childhood cancer remained very low in both groups. Experts note that the association may partly reflect indication bias, meaning sicker or more vulnerable pregnancies are more likely to receive steroids. ACS continue to play a vital role in protecting premature infants, and further research is needed to better understand long-term outcomes and guide shared decision-making.
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