Understanding Your Fertility Window

When we were kids learning about sex ed, we were taught not to have sex because you WILL get pregnant at any point in your cycle. I believed this for years, worried that I could get pregnant no matter where I was in my cycle when I had sex. Getting pregnant was just that easy. It wasn’t until years later that I learned that wasn’t the case, and there is a small fertile window where women are likely to conceive if they have sex.

Understanding Your Cycle

Let’s start with the basics. Your cycle begins on the first day of your period and lasts until the first day of your next period.₁ Every woman’s cycle is different, lasting from 21 – 45 days. The menstrual cycle can be broken down into four phases.

1. The first phase of your cycle is menstruation, your period. The menstrual phase is when your uterine lining sheds through your vagina.₂
2. The next phase is the follicular phase, which lasts from the first day of your cycle until ovulation. The fluid-filled sacs – follicles – in your ovaries have immature eggs. Of these follicles, only one will mature, as will the egg.₃
3. This leads us to the next phase, ovulation. During ovulation, the mature egg is released from an ovary and travels along the fallopian tube towards the uterus.₄ Every woman’s cycle is different, but this usually occurs about two weeks before your period.₅
4. The final phase in your cycle is the luteal phase. During the luteal phase, your uterus prepares for pregnancy. The mature follicle forms into the corpus luteum – a cyst that forms on the ovary and produces progesterone.₆ If the egg is fertilized, the corpus luteum will produce progesterone for 12 weeks until the placenta takes over. If the egg is not fertilized, the corpus luteum starts to break down around ten days after the mature egg is released, and you will shed your uterine lining, completing the menstrual cycle and starting your next one.₇

What Does This Mean if You’re Trying to Conceive?

There are a few points in your cycle where you are most fertile. The days leading up to and during ovulation are your most fertile days.₈ This does not mean there are points in your cycle where you are 100% safe from pregnancy if you have sex without protection,₉ as sperm can survive for up to five days within the female.₁₀ If you have a short cycle and ovulate early, then it is possible to get pregnant if you have sex during your period.₁₁

Our bodies don’t work like clockwork. Our cycles can vary from month to month,₁₂ which is why it is difficult to tell if there’s a point in your cycle where you are likely/not likely to get pregnant. However, if you are trying to conceive, the days leading up to and during ovulation is the point in your cycle where you are most fertile.₁₃

References

1, 8, 9, 11, 13 Can I get pregnant just after my period has finished? NHS choices. Accessed November 6, 2023. 

2, 4, 5 Department of Health & Human Services. Menstrual cycle. Better Health Channel. April 26, 2001. 

Accessed November 6, 2023. https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/menstrual-cycle. 

3 Professional CCM. Follicular phase of menstrual cycle: Hormone levels & length. Cleveland Clinic. Accessed 

November 6, 2023. https://my.clevelandclinic.org/health/body/23953-follicular-phase. 

6, 7 Professional CCM. Corpus luteum: Development, anatomy & function. Cleveland Clinic. Accessed 

November 6, 2023. https://my.clevelandclinic.org/health/body/21849-corpus-luteum. 

10 Gargollo, M.D. PC. Sperm: How long do they live after ejaculation? Mayo Clinic. May 5, 2022. Accessed 

November 6, 2023. https://www.mayoclinic.org/healthy-lifestyle/getting-pregnant/expert-answers/pregnancy/faq-20058504#:~:text=The%20life%20span%20of%20sperm,decades%20when%20semen%20is%20frozen. 

12 Levine B. What are irregular periods: Treatment, pregnancy, and more. EverydayHealth.com. May 11, 2020. 

Accessed November 13, 2023. https://www.everydayhealth.com/pms/irregular-periods.aspx#:~:text=Menstrual%20cycles%20don’t%20always,vary%20from%20cycle%20to%20cycle.