Afti, Ismi Mulya, et al. “Differences in Levels of Vitamin D, Human Placenta Lactogen (hPL) and Estradiol in Normal Pregnancy and 1st Trimester Abortion”. Majalah Kedokteran Andalas, vol. 45, no. 4, Oct. 2022, pp. 524-30, doi:10.25077/mka.v45.i4.p524-530.2022.