A new effect of intravenous iron treatment in pregnancy: contraction in nonstress test and timing of labor

TL;DR

This study finds that intravenous iron treatment in late-term pregnancies may cause contractions and potentially lead to earlier births, especially in women with a history of cesarean.

Contribution

The study identifies a new potential effect of intravenous iron treatment in pregnancy: inducing contractions and possibly early labor.

Findings

72.1% of pregnant women showed regular contractions in nonstress tests after intravenous iron treatment.

Women with a history of cesarean delivered earlier after treatment compared to others (p<0.001).

Abstract

The aim of this study was to elucidate the cause and results of contractions occurring in term pregnant women receiving intravenous iron therapy.

During 2019–2020, 136 pregnant women beyond 35 weeks of gestation, who received intravenous iron treatment due to iron deficiency anemia, were included through retrospective screening. Iron deficiency anemia was defined as having hemoglobin levels <10 g/dL and ferritin levels <15 ng/mL, and the pregnant women underwent nonstress test before and after treatment.

The average treatment week for the pregnant women was 36.82±0.74, and the presence of regular contractions in post-treatment follow-up nonstress tests was 72.1% (n=98). The average week of birth was 38.48±1.60. Pregnant women with contractions who had previous cesarean were found to have a mean delivery week of 36.82±0.67, which was statistically significant earlier than for nulliparous and multiparous women (p<0.001).

In pregnant women with iron deficiency anemia who were beyond 35 weeks, temporary regular contractions may be observed in the nonstress test following intravenous iron replacement. We think that this effect may lead to early term birth in pregnant women with a history of cesarean section. It needs to be confirmed by further prospective studies and animal studies.