The short answer is that it’s very unlikely you’ll become pregnant when you’re on your period. However, it’s also not impossible to get pregnant while you have your period.
Can you get pregnant on your period? Yes: In order to understand how it's possible, we’ll first explain the time of your menstrual cycle when you’re most likely to get pregnant.
When You’re Most Likely to Get Pregnant
During reproductive ages, the ovary releases an egg every month. This event occurs when ovary follicles rupture and release the oocyte which travels to the fallopian tube and becomes an ovum or egg.
The rupture of the ovary follicles can cause some light spotting and some can even feel it happen in their body. However, for the vast majority of women, the moment of ovulation usually goes unnoticed.
The process of ovulation is controlled by the hypothalamus of the brain and through the release of hormones. This means that ovulation can be impacted by hormone levels and stressors.From jet lag to thyroid disorders, the sensitive process of ovulation can be disrupted when your body undergoes changes. Hormonal contraceptives inhibit ovulation to prevent pregnancy.
After the oocyte is released from the ovary, it moves into the fallopian tube. At this point it is called an ovum or egg. The egg stays in the fallopian tube for about 24 hours, waiting for a single sperm to fertilize it.
If the egg is not fertilized by sperm during that time (and pregnancy does not occur), it disintegrates (breaks down) and menstruation (your menstrual period) begins 11-16 days later.
Signs of Ovulation
Ovulation usually goes unnoticed in many but there are some ovulation symptoms that most women can learn to track or pay attention to. These include:
- Your basal body temperature falls
- Discharge changes: If your cervical mucus is…
- Dry or sticky: It’s unlikely you’re ovulating
- Creamy cervical mucus: Ovulation may be coming
- Wet or watery: Ovulation may start soon
- Wet and stretchy (egg white texture): You may be at your day of ovulation
- Your cervix softens and opens up
- You may experience a slight twinge / cramping called Mittelschmerz
- Increased libido or sex drive
How Long Do You Ovulate For?
The “fertile window” lasts between 12 and 24 hours. That's how long the egg released by the ovary is viable for fertilization.
Complicating Factors: Why You Can Still Get Pregnant While You Have Your Period
Our bodies don’t necessarily follow “the rules” and many women experience an irregular cycle and/or period. There are some complicating factors:
(1) Sperm Survival
Sperm can live 3-5 days after sexual intercourse and ejaculation. This means that even though you’re not ovulating when you have intercourse, if you are fertile 5 days later the sperm can still fertilize your ovum, resulting in pregnancy.
(2) Your Menstrual Cycle Isn’t a Clock
As we mentioned earlier, a woman’s menstrual cycle is not an exact science. The first day of a menstrual cycle is calculated from the first day of your period. Between women, the length of a menstrual cycle can vary extremely.
- The average menstrual cycle is 28 days (ovulate around day 14)
- A short cycle can be 21 days (ovulate around day 7)
- A long cycle can be 35 days (ovulate around day 21)
Moreover, even at the individual level, cycles can be variable. One woman might, for example, have a very average menstrual cycle of 28 days.
However, many other factors can throw her cycle off on any given month. These factors could include:
- Stress levels
- Sleep schedule (e.g. insomnia or jet lag)
- Lifestyle and weight
If you experience a very short cycle (for whatever reason), considering that sperm can remain active for 5 days after intercourse, there is a chance that pregnancy could occur.
(3) You Might Confuse Other Vaginal Bleeding for Your Period
Another reason you might become pregnant while on your period is that you are experiencing vaginal bleeding that’s not a period. This might cause you to:
- Think you’re having your period, when you’re not
- Miscalculate your fertile window because you misidentify a period
Some of the common causes of vaginal bleeding outside of a period include:
- Trauma or medical examination
- Medications side effects
- Sexually Transmitted Infection (STI), including chlamydia, gonorrhea, and genital warts.
- Pelvic Inflammatory Disease (PID)
- Uterine fibroids or polyps
- Polycystic ovary syndrome (PCOS)
- Blood clotting disorders, like von Willebrand disease.
- Other health conditions, like hypothyroidism, liver disease, or chronic kidney disease.
If You’re Trying to Get Pregnant...
Having sex during your period is not going to carry the greatest likelihood of getting pregnant. Of course, you can have sex at any time for pleasurable reasons. But if your goal is becoming pregnant, you’ll want to calculate your ovulation day and have sex during the days around this date.
If You Want to Avoid Getting Pregnant...
If you don’t want to get pregnant, there really is no 100% safe time to have unprotected sex. Even with protection, no method of birth control is 100% failsafe.
Understanding and tracking your cycle can definitely help you decrease odds of an unwanted pregnancy. Still, most healthcare providers still advocate for the use of a form of birth control or contraception to prevent unwanted pregnancy (and STIs).
To discuss what form of contraception would work for you and your partner, chat with your doctor.