Yadav, Richa, and Urmila Singh. “Study of Changes in Levels of Salivary Estriol and Progesterone in Preterm Labor in Comparison to Normal Pregnancy”. International Journal of Reproduction, Contraception, Obstetrics and Gynecology 8, no. 12 (November 26, 2019): 4660–4667. Accessed October 13, 2025. https://www.ijrcog.org/index.php/ijrcog/article/view/7556.