The goal of this clinical trial is to find out whether giving vitamin D to pregnant women who had pre-eclampsia in a previous pregnancy helps prevent the condition from coming back. The main question it aims to answer is: Does vitamin D supplementation reduce the chance of pre-eclampsia recurring in pregnant women with a history of pre-eclampsia? To answer this question, pregnant women attending the antenatal clinic at the Department of Obstetrics and Gynaecology, Nishtar Hospital Multan will be invited to join the study. Participants will be randomly assigned to two equal groups: * Vitamin D group: will take 4,000 IU of oral vitamin D until 36 weeks of gestation. * Placebo group: will receive a pill identical in appearance, taste, and consistency but without vitamin D. While on the study medication, each woman will visit the clinic every two weeks. At each visit, her blood pressure will be measured, and if it is 140/90 mmHg or higher, a urine test will check for protein to identify pre-eclampsia as per hospital protocol. Any diagnosis of pre-eclampsia will lead to standard care, and the outcome will be recorded. At the end, researchers will compare how many women in each group developed recurrent pre-eclampsia. This study will help answer whether vitamin D supplementation can safely reduce the risk of pre-eclampsia returning in women with a prior history - a question important for improving pregnancy outcomes and maternal health.