The goal of this clinical trial is to determine whether vitamin D supplementation can reduce the recurrence of preeclampsia in pregnant women with a previous history of preeclampsia.

The main questions the study aims to answer are:

- Does daily vitamin D supplementation reduce the recurrence of preeclampsia compared with a placebo?

Researchers will randomly assign 146 eligible pregnant women to receive either vitamin D supplements or a placebo. The two groups will be compared to determine whether vitamin D lowers the risk of recurrent preeclampsia.

Participants will:

• Be randomly assigned to receive either 4000 IU oral vitamin D once daily or a matching placebo.
• Take the assigned study medication daily until 36 weeks of gestation.
• Attend follow-up visits every 2 weeks for blood pressure measurement and clinical assessment.
• Have serum vitamin D levels measured every 4 weeks to monitor for vitamin D toxicity.
• Undergo urine testing for protein if blood pressure is elevated to assess for preeclampsia.

The results of this study will help determine whether vitamin D supplementation is an effective and safe strategy for preventing recurrent preeclampsia in women at high risk.