Generally, your period arriving is a pretty solid indication you aren’t pregnant, but generally is not always. Bleeding during pregnancy which can be mistaken for a period while pregnant is possible– most especially in the first cycle after conception. How?
Note: This article covers bleeding that looks like a period while pregnant in very early pregnancy, typically before pregnancy is confirmed. You can find more causes of bleeding during pregnancy in the first trimester here and the second and third trimester here.
Conception that occurs close to menstruation or low progesterone levels may cause what looks like a period while pregnant:
Conception may not occur until mere days before your period is due if you have a short menstrual cycle or don’t ovulate mid-cycle.
For example, let’s say you are regularly maintaining a 26 day cycle. Chances are you’ll ovulate around day 13. Even if you had unprotected sex on that day and sperm found egg later that day, it would still take the fertilized egg six to twelve days to reach and implant in your uterine lining. By this timeline, your body wouldn’t know to continue producing the hormone progesterone that ceases menstruation until somewhere between day 20 to 25 of your cycle. This could leave as little as one day between conception and menstruation. If those hormone levels are insufficient, such as in a situation of low progesterone from luteal phase defect, or had already begun to fall, you could have what seems like a lighter than usual period while pregnant or even one that seems entirely normal and wouldn’t think you missed a period until you were already around six weeks pregnant. This type of bleeding is often referred to as “break through bleeding,” and is the most common type of bleeding mistaken for a period while pregnant.
Break through bleeding is usually seen during the first cycle after conception, but may continue in the first trimester. As this can be indicative of low progesterone, it should be evaluated by a doctor, in fact, any bleeding during pregnancy should. It should also be noted that even if there is bleeding when your period is due, if you are pregnant, ovulation will not occur again. This type of bleeding is not a true period while pregnant. You cannot have what is technically referred to as a period while pregnant, because your uterine lining is not entirely shed along with the egg or your baby would be lost. Basal body temping can be a great way to catch such a situation, because a rise in temperature confirms ovulation and prolonged high temps for 16 days can be a way to confirm pregnancy, bleeding or not.
Implantation bleeding may be mistaken for a period while pregnant:
Many women also mistake implantation bleeding for a period while pregnant. If you followed the same example above, and usually had a light period, and you had spotting on day 23, you may think that was your period simply a day or two early. Implantation bleeding varies from woman to woman, but a heavy flow is almost never implantation bleeding. You can read a full article on telling the difference here.
Sporadic bleeding during pregnancy may be mistaken for a period while pregnant:
Finally, numerous other causes can result in bleeding during pregnancy. I personally have known quite a few women who experienced periodic bleeding for the first several months of their pregnancy that seemed like a period while pregnant. Some examples of causes of bleeding during pregnancy that may be mistaken for a period while pregnant include cervical changes, sex, placenta problems, carrying multiples, and infection. You can read about these in more detail in the posts link at the beginning of this article for bleeding during a confirmed pregnancy. In some cases, no reason is found and nothing is abnormal or wrong at all. Another note here though, timely monthly bleeding in pregnancy is uncommon. When bleeding occurs beyond that first month, it’s usually erratic, not the sort of thing you can see a clear pattern in like a regular monthly period.
It’s important to understand that bleeding doesn’t guarantee that you aren’t pregnant, but then it’s usually a pretty good indication that you aren’t. Pay attention to your body, trust your instinct, and when in doubt, act pregnant until you’re sure you aren’t.
Did you experience bleeding during your pregnancy or did you have bleeding and think you were pregnant, but weren’t? We want to hear your story. We have a page set up for them here.
Note: The extensive comment base on this article led me to write its sister articles, “Missed Period Negative Pregnancy Test Explanation” , “Late period, missed period, irregular period, Oh, Why!?,” “When to Take a Pregnancy Test,” and “Am I Pregnant? Calculating Your Chances of Pregnancy” which offer other explanations for irregular bleeding or missed periods in-depth and may help you assess whether or not you could be pregnant.
I do my best to respond to comments within 24 hours. All comments are moderated, so I reply to each and every one as I approve them, but please remember, I am not a doctor nor a replacement for medical care. I cannot tell you if you are or are not pregnant over the Internet, and I cannot diagnose you over the Internet either. I do have a medical background (medical assisting) and am a mother of four who struggled with infertility as well as multiple miscarriages, but I am not a doctor nor claim to be one.