Firdanisa, A.H. et al. 2022. Differences in Levels of 25-hydroxyvitamin D, Human Chorionic Gonadotropin (hCG), and Progesterone in Normal Pregnancy and First Trimester Abortion. Majalah Kedokteran Andalas. 45, 4 (Oct. 2022), 531–537. DOI:https://doi.org/10.25077/mka.v45.i4.p531-537.2022.