Objective: (1)To analyze of efficacy of metformin in pregnant women with POCS regarding occurrence of gestational diabetes mellitus (2) To analyze parity distribution for efficacy of metformin regarding occurrence of gestational diabetes mellitus in pregnant women with POCS. Study Design: Descriptive Cases Series. Setting: Sheikh Zaid Hospital, Lahore. Period: July 1, 2019 to December 31, 2019. Methods: Till delivery 200 pregnant ladies were followed up to see if they developed GDM or not. A pre-prepared form was used to record metformin efficacy frequency and GDM in pregnant ladies with PCOS. For efficacy and parity (qualitative variables), percentages and frequencies were got calculated using SPSS.16. Results: Thirty two (16%) women got ‘0’ parity. Forty four (22%) got ‘1’parity. Fifty (25%) got ‘2’ parity. Forty two (21%) got ‘3’parity.While thirty two women (16%) got ‘4’ parity. Twenty two (78.57%) was efficacy for nulliparous patients. Thirty three (76.74%) was efficacy for primiparous patients. One hundred nine (84.50%) was efficacy for multiparous patients. Insignificant difference was noted as p was more than 0.05. In one hundred sixty six (83%) women metformin efficacy got achieved. Conclusion: Multiparous patients with PCOS showed relatively more efficacy (84.50%) of metformin against gestational diabetes mellitus while twenty five percent pregnant women with PCOS with a thorough use of metformin delivered two live neonates.