A normal menstrual cycle can be divided into follicular and luteal phases, which are separated by ovulation. 

The follicular phase starts on the first day of menstruation and ends when you start to ovulate. The luteal phase happens after ovulation and before your period starts. 

Ovulation is when the ovary releases an egg so it can be fertilized by a sperm in order to make a baby. You are most likely to get pregnant if you have sex without birth control in the three days before and up to the day of ovulation. Ovulation usually occurs regularly, around day 14 of a 28-day menstrual cycle. 

According to the American College of Obstetricians and Gynecologists (ACOG), you can get pregnant if you have sex anywhere from 5 days before until 1 day after ovulation. And this time period is usually called the ‘fertile window’.

How do I know if I’m ovulating?

A few days before you ovulate, your vaginal mucus changes and becomes more slippery and clear. This type of mucus helps sperm move up into your uterus and into the fallopian tubes where it can fertilize an egg. Some women feel minor cramping on one side of their pelvic area when they ovulate. Some women have other signs of ovulation.

Reference:

1. Mesen, T. B., & Young, S. L. (2015). Progesterone and the luteal phase: a requisite to reproduction. Obstetrics and gynecology clinics of North America, 42(1), 135–151. https://doi.org/10.1016/j.ogc.2014.10.003

2. American College of Obstetricians and Gynecologists. (2020). Fertility Awareness-Based Methods of Family Planning. Available at: https://www.acog.org/womens-health/faqs/fertility-awareness-based-methods-of-family-planning

3. Office on Women’s Health, U.S. Department of Health and Human Services. (2021). Your menstrual cycle. Available at: https://www.womenshealth.gov/menstrual-cycle/your-menstrual-cycle (Accessed: 06 June 2022).