For most women, “menstrual cycle” means “period” — buying pads, tampons or cups, and maybe experiencing cramps or mood swings, but in fact the menstrual cycle is the time from the first day of your period all the way to the day before your next period starts. You probably haven’t thought about what happens during the rest of your menstrual cycle since your high school health class. But understanding the whole menstrual cycle can help clear up misconceptions and confusion, specifically surrounding getting pregnant.
A big misconception is the belief that most women have a 28-day cycle every month. In a recent study of cloud data collected from Bluetooth-connected ovulation tests of more than 32,000 women representing more than 75,000 cycles, 25.3% of users described their cycle length as 28 days, but only 12.4% of users had a 28-day cycle. Most women (87%) had cycles ranging from 23 to 35 days, and 52% of women had cycles that varied by five days or more in length. Your cycle length impacts the timing of ovulation.
Consider this a quick guide to how a typical menstrual cycle influences the chances of pregnancy and the links between menstruation, ovulation and conception.
Day 1 of your cycle
This is the first day of your period, also known as menstruation. Your body begins breaking down the lining of your uterus. Bleeding typically lasts three to seven days, and it’s common to have cramps and pain in your stomach and lower back, especially early on. During menstruation, your body is already starting to prepare for ovulation. Your pituitary gland, located in your brain, produces FSH (Follicle-stimulating hormone), which kicks your ovaries into gear. Fluid-filled follicles develop on your ovaries. Each follicle contains one egg.
The follicular phase leading up to ovulation
During a typical follicular phase, only one follicle keeps growing and starts to release increased levels of estrogen. Usually by day eight, you’re feeling pretty good, partly because estrogen increases endorphins and partly because your period is over. But that estrogen is doing more than affecting your mood. It’s also alerting your uterus, essentially saying, “Hey, we may need you!” In response, the uterine lining becomes thick with nutrients and blood, ready to receive a fertilized egg.
Ovulation (aka when you are most fertile)
Your estrogen levels might be sky-high right now, which triggers an LH (luteinizing hormone) surge. This surge forces your follicle to rupture and release its egg, sending it through your fallopian tubes. This is ovulation. Your egg will only live 12 to 24 hours, but — and this is important — sperm can live inside you for three to five days. If you have sex on the day you ovulate or a few days prior to ovulation, the sperm just hangs out, waiting for an egg. This is why timing is so important. If the egg and sperm rendezvous, pregnancy is possible.
After you ovulate: The luteal phase
Your body is now entering what we call the luteal phase. Your follicle begins making more progesterone, a hormone that helps the lining of your uterus store even more blood and nutrients, just in case it receives a fertilized egg. If the egg is fertilized, it will continue traveling through the fallopian tube and then attach itself to your uterine lining, about a week after fertilization. The fertilized egg implants and starts producing the hCG (human chorionic gonadotrophin) hormone, which keeps your estrogen and progesterone levels high, preventing the uterine lining from shedding until the placenta is ready to take over.
Leading up to your next period
If you’re not pregnant there is no hCG, so your estrogen and progesterone levels drop, which does two things: the thick uterine lining begins to break down and you may experience PMS (premenstrual syndrome). That unfertilized egg? It breaks apart and leaves your body along with the blood and tissue from your uterine lining. Once bleeding starts, you’re back at day one of your cycle.
- Bull, J. R., Rowland, S. P., Scherwitzl, E. B., Scherwitzl, R., Danielsson, K. G., & Harper, J. (2019). Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. npj Digital Medicine, 2(1). https://doi.org/10.1038/s41746-019-0152-7
- Infertility. (2019, April 1). Office on Women’s Health. https://www.womenshealth.gov/a-z-topics/infertility
- Periods and fertility in the menstrual cycle. (2021, February 12). National Health Service. https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/
- Reed, B. G., MD, & Carr, B. R., MD. (2000). The Normal Menstrual Cycle and the Control of Ovulation. In K. R. Feingold, B. Anawalt, & A. Boyce (Eds.), Endotext [Internet]. MDText.com, Inc.
- Soumpasis, I., Grace, B., & Johnson, S. (2020). Real-life insights on menstrual cycles and ovulation using big data. Human reproduction open, 2020(2), hoaa011. https://doi.org/10.1093/hropen/hoaa011
- What happens during the typical 28-day menstrual cycle? (2018, March 16). Office on Women’s Health. https://www.womenshealth.gov/menstrual-cycle/your-menstrual-cycle#3