Effects of different folic acid supplementation doses on subsequent pregnancy outcomes in women with a history of pregnancy loss: study protocol for a multicentre randomised controlled trial

Introduction Folic acid is crucial for fetal development, particularly during early pregnancy. Studies suggest that high folic acid intake (≥800 µg/day) may be associated with a reduced risk of miscarriage. However, the impact of an 800 µg dose on pregnancy outcomes in women with prior pregnancy loss currently remains unclear.Methods and analysis We will conduct a multi-centre randomised controlled study comparing 800 µg and 400 µg in women with previous pregnancy loss. The primary outcome is live birth. Secondary outcomes include early pregnancy loss, ongoing pregnancy at 24 gestation weeks, homocysteine (Hcy) reduction, maternal and perinatal outcomes. We plan to recruit 1116 women (558 women per group). Data analysis will follow the intention-to-treat principle and per-protocol. Subgroup analysis will be conducted based on Hcy levels, previous pregnancy losses and body mass index.Trial registration number ChiCTR2500100255.