implantation bleeding

Implantation Bleeding vs. Your Period: Decoding this Early Sign of Pregnancy

If you’re trying to get pregnant, the two weeks between ovulation and your scheduled period can be excruciating. If and when your period arrives, you know you have to start all over again. But did you know that blood in your underwear could actually mean you conceived? Instead of Aunt Flow it could be her pregnancy-related cousin: implantation bleeding.

What Is Implantation Bleeding?

Most women ovulate halfway through their menstrual cycle, and if you don’t get pregnant then, you’ll get your period about two weeks after that. If a sperm does successfully fertilize the egg you released at ovulation, you have conceived. This newly created embryo will then travel to your uterus and burrow itself into the lining, if all goes according to plan. When this occurs, the embryo may agitate the blood cells in your lining and cause blood to be released from your body. The apparent release of that blood is known as implantation bleeding and it is an early pregnancy symptom.  

There are a few ways you can distinguish implantation bleeding from your period:

  • Timing: Implantation bleeding happens six to 14 days after conception. It typically happens before your period would normally arrive.
  • Color: Implantation bleeding is often pink or brown, instead of bright red.
  • Amount of blood: Implantation bleeding produces spotting, not a heavy flow. It usually lasts one to three days. That’s because the embryo has displaced only a small portion of your uterine lining. When you get your period, on the other hand, you shed the whole thing.

How Common Is Implantation Bleeding?

As many as one in four pregnant women may experience implantation bleeding. In its run down of pregnancy symptoms, the National Institute of Child Health and Human Development cites research that shows 25 percent of pregnant women experience some spotting that is lighter in color than normal menstrual blood and which occurs about six to 12 days after conception. You can’t say for certain that each instance of early bleeding is caused by implantation, but it is a common explanation.

As many as one in four pregnant women may experience implantation bleeding.

Typically, this type of early bleeding is not something to worry about. I spoke to Dr. Emily Harville and Dr. Allen Wilcox, co-authors of a paper on vaginal bleeding in very early pregnancy. In their study, nine percent of women with clinical pregnancies reported bleeding in the first eight weeks of pregnancy. And about 85 percent of these pregnancies continued to a live birth. “These data suggest that a few days of bleeding in early pregnancy is not a rare event, and furthermore that such bleeding has little relevance to the ultimate success of the pregnancy,” they concluded.

As far as the exact timing of this pregnancy symptom, the study found that bleeding tended to occur around the time when women would expect their periods, although rarely on the day of implantation. Dr. Harville, who researches reproductive questions at Tulane University, told me: “We had very specific information on when implantation was occurring, and ‘implantation bleeding’ did not usually occur on the actual day of implantation.” This finding suggests that there may be a delay between implantation and when the bleeding appears, which makes sense since the blood would have to travel through your body. It could also indicate that other causes can explain bleeding in very early pregnancy.

Other Causes of Bleeding in Early Pregnancy

Besides your period or implantation bleeding, there may be other explanations for bleeding in early pregnancy.  The American College of Obstetricians and Gynecologists explains that the cervix may bleed more easily during pregnancy because more blood vessels are developing in this area. Sexual intercourse or a pelvic exam could also trigger harmless light bleeding. A subchorionic hemorrhage, or blood clot on the wall of the uterus, may also be to blame. Such blood clots typically resolve themselves.

Finally, complications like an ectopic pregnancy (when the fertilized egg implants outside of the uterus) or threatened miscarriage due to chromosomal problems can also lead to early bleeding. If you see blood and suspect you might be pregnant, it’s always a good idea to contact your doctor. Now you know: don’t just assume it’s your period.

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