Dhar, A., and I. Kaul. “Value of PI of Uterine Artery at 23-24 Weeks in the Prediction of Adverse Pregnancy Outcome”. International Journal of Reproduction, Contraception, Obstetrics and Gynecology, vol. 6, no. 12, Nov. 2017, pp. 5435-9, doi:10.18203/2320-1770.ijrcog20175256.