Can you get pregnant on your period?

If you are wondering whether you can get pregnant while on your period, the answer is not as simple as you think. “The answer to the question has more to do with understanding your cycle,” said Lyndsey Harper, MD, FACOG, IF, clinical assistant professor at the Texas A&M College of Medicine. “Many women think they know their menstruation cycle, and therefore their fertility cycle, but the truth is not all vaginal bleeding is a true period.”

Fertility awareness as a method of birth control

All birth control methods can fail, even those with the highest effectiveness rate like intrauterine devices (IUD) or tubal ligation. People should understand how well each option works prior to deciding upon a method of contraception.

When using fertility awareness as a method of birth control, fewer than five out of 100 women will become pregnant during the first year of perfect use. That being said, this method of birth control is very difficult to do without error.

When tracking your cycle, the first day should be when you begin bleeding. For most women, ovulation—the release of the egg from the ovaries—occurs around day 14. “Some women may bleed for up to 10 days. Therefore, they may become fertile only four days after their period ends,” Harper said. “Some women even have earlier ovulations and some have later ovulations.”

Ovulation and fertility: How do I know?

Because periods can be different lengths and not all bleeding is a period, it can be confusing to track your ovulation. “The best way to track your ovulatory cycle is by watching it for three to four months,” Harper said. To track, Harper recommends determining the average time between the start of one period to the start of the next. Because this is an average number, it does not have to be exactly the same every month. “If this average number is between 21 and 35 days, then you can divide that number in half, which is MOST LIKELY, but not guaranteed, to be the time of ovulation.”

Once you have monitored a few cycles and think you know when you are ovulating, check on your vaginal discharge. “Around the time of ovulation, discharge becomes thick and stretchy–just like an uncooked egg white,” Harper mentioned. “This is the best way to verify that you are on track when it comes to predicting ovulation.” If you take a birth control pill, then you do not ovulate at all and do not need to pay attention to discharge.

Cervical mucus accepts, filters, prepares and releases sperm for the successful fertilization of an egg. If you do not want to become pregnant and are not using another birth control, Harper says it is best to avoid intercourse the week you notice the mucus.

Top reasons your vaginal bleeding may not be a period

One of the biggest margins for error while using fertility awareness as a method of birth control comes from a misidentified period. Not all vaginal bleeding is a period. A woman may bleed from a hormonal imbalance, cervical lesion, recent trauma and even pregnancy.

“If you are tracking your menstrual cycle and the bleeding is consistent in terms of heaviness, color and timing, then you can likely count on it being your period,” Harper said. “However, there are many women that find it difficult to track their period because irregular bleeding can be due to illness or another underlying cause.”

If you are having difficulty or need help starting, talk with your OB-GYN or primary care provider.

Fertility tracking for women with PCOS and irregular periods

If women are not ovulating or ovulating irregularly, as in the case of polycystic ovary syndrome (PCOS), they may experience irregular bleeding.  Women with PCOS have bleeding that occurs randomly, not in response to a true cycle. As a result, women with PCOS cannot use their period to track their cycle. They would be better suited to discuss alternative methods of tracking fertility with their health care provider.

Similarly, women who experience irregular periods should not count on using their period to track their fertility. An average period cycle lasts 21 to 35 days from the start of one period to the start of the next period. If your periods fall out of this timeframe, then they may be irregular and not associated with ovulation.

“Women may experience irregular periods for a variety of reasons like being underweight or constant and intense exercise,” Harper said. “However, irregular periods may be an indicator of an underlying health issue like PCOS. Speak with your provider if you believe you have an irregular menstrual cycle.”

So…can I get pregnant while on my period?

It is exceedingly unlikely to get pregnant while on your period. If your vaginal bleeding is a true “period,” then this is an indicator that you are having regular ovulatory cycles and can be your most valuable insight into your fertility cycle. If you are having really long cycles or irregular bleeding, the chances of becoming pregnant can change because it is less clear where you are in the cycle.

“It can be difficult to figure out your fertility cycle, but your provider is there to help you,” Harper said. “Whether you want to be pregnant or not, you should try to understand your cycle. Once you do, then you can make better-educated decisions about your sexual health.”