Can You Be Pregnant While Having Periods?
Yes, you can be pregnant even if you experience bleeding that seems like a period—what you're seeing is likely not a true menstrual period but rather implantation bleeding or other pregnancy-related bleeding that can be easily mistaken for menstruation. 1
Understanding Why This Happens
True Periods vs. Pregnancy Bleeding
A true menstrual period occurs only when you are not pregnant, as it represents the shedding of the uterine lining when no pregnancy has occurred. 2
Implantation bleeding can occur 6-12 days after fertilization when the fertilized egg attaches to the uterine lining, and this is typically lighter and shorter than a normal period but can be mistaken for one. 1
Hormonal fluctuations in early pregnancy can sometimes cause light bleeding that coincides with when you would expect your period, leading to confusion about whether you're pregnant. 1
In rare cases, some women experience light bleeding throughout early pregnancy that occurs around the time of their expected menstrual cycle. 1
The Clinical Evidence
Timing and Ovulation
During a typical 28-day cycle, ovulation occurs between days 9-20, making it biologically unlikely that you would have a true period and then become pregnant within the same cycle. 2, 1
Healthcare providers can be reasonably certain a woman is not pregnant if she is ≤7 days after the start of normal menses, which means normal menstrual bleeding is fundamentally inconsistent with early pregnancy. 2
When Pregnancy Can Be Detected
Most FDA-approved urine pregnancy tests detect hCG at 20-25 mIU/mL, which is sufficient to detect most pregnancies by the time of a missed period. 2, 3
By 7 days after the expected period, 98% of pregnancies will test positive. 4
However, 10% of clinical pregnancies have not yet implanted by the first day of the missed period, meaning they cannot be detected even with the most sensitive tests. 5
What You Should Do
If You're Experiencing Bleeding and Suspect Pregnancy
Take a pregnancy test if the bleeding you experienced was different from your normal period (lighter, shorter, different timing, or unusual characteristics). 1
Wait and retest if you get a negative result but still have pregnancy symptoms, as some studies show an additional 11 days past the expected menses may be needed to detect 100% of pregnancies. 2, 3
Calculate pregnancy dating from your last true menstrual period, not from any bleeding that occurred after conception. 1
Critical Pitfalls to Avoid
Don't assume bleeding means you're not pregnant—this is the most common misconception and can delay prenatal care or lead to inadvertent exposure to harmful substances. 1
Women with irregular cycles may have particular difficulty distinguishing between normal cycle variations and early pregnancy bleeding. 1
A negative pregnancy test doesn't definitively rule out pregnancy if taken too early, especially if you've had recent unprotected intercourse within the last 5 days. 2, 3