Sahoo, I., M. Dey, and J. A. “Association of First Trimester Serum Level of Placental Growth Factor (PlGF) and Cervical Length With Onset of Preterm Labour”. International Journal of Reproduction, Contraception, Obstetrics and Gynecology, vol. 8, no. 4, Mar. 2019, pp. 1641-5, doi:10.18203/2320-1770.ijrcog20191234.