Objective: To see the correlation of menstrual cycle factors with time to achieve a pregnancy, in a cross sectional survey of a tertiary care hospital in karachi.

Study Design: A cohort study and convenience sampling technique was used.

Place and Duration of Study: The outpatient department of OBGYN, The Dow University Hospital, from June 2020 till June 2021.

Methodology: All the women who were coming to antenatal clinic and were eligible with the inclusion criteria were interviewed in the OPD (outpatient department).The research instrument used for the study was a self-developed questionnaire, which comprised of demographics, reproductive and medical history and life style and behavioral factors in close ended questions on the menstrual cycle patterns.

Results: among the participants with age of menarche ≤14 years old 98.2% reported for regular menstrual cycle, 6.5% reported for less than 25 days of cycle length, 5.3% reported for less than 3-days of bleeding duration, 68.8% were currently pregnant, out of which 53% conceived after trying for conception between 6-9 months. , in samples with menarche age more than 15-years old 90.3% reported for regular menstrual cycle, 33.3% reported for 27-29 days of cycle length, 31.9% reported for less than 3-days of bleeding duration, 72.2% were currently pregnant, 37% conceived after trying for conception from 6-9 months.

Conclusion: Therefore from this study we concluded that late menarche (>15 years), prolonged cycles and decrease bleeding days are the associated factors with decrease fecundity in terms of prolonged time to achieve pregnancy in our study population.

KeyWords: Menarche, Time to pregnancy, fertility, menstrual cycle.