Potential Causes of Bleeding During Pregnancy

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It is not possible to have a true menstrual period during pregnancy. Your hormone levels during pregnancy will change to prevent you from menstruating, and it is not possible for your body to shed its entire uterine lining while maintaining a pregnancy.

It is, however, possible to have menstrual-like bleeding for a variety of reasons during pregnancy.

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Decidual and Implantation Bleeding

Women who report having periods during an otherwise normal pregnancy are usually experiencing a phenomenon that is sometimes called ​decidual bleeding, in which a small part of the uterine lining might shed for the first few months of early pregnancy at the time that the woman would otherwise have had her period.

Decidual bleeding is not a true menstrual period, but it can look similar enough to cause women experiencing it to not realize that they are pregnant until fairly far along in the pregnancy.

Another possible explanation for having bleeding that looks like a period in very early pregnancy is implantation bleeding, which is spotting that may occur around the time of the first "missed" menstrual period. Implantation bleeding would occur only during the first month of pregnancy, however.

Note, however, that bleeding during pregnancy should always be reported to a doctor in order to rule out miscarriage or other complications. Decidual bleeding does occur in some women but is fairly rare. Implantation bleeding usually lasts only a day or two. So seeing a doctor is your best bet for ruling out miscarriage and figuring out the reason for your bleeding during pregnancy.

Note that "decidual bleeding" is not a common medical term; your doctor may simply refer to this bleeding as "first-trimester bleeding."

Causes of First-Trimester Bleeding

Bleeding during the first trimester is understandably dismaying. Fortunately, many women who bleed early on during pregnancy go on to deliver healthy babies. Nevertheless, it's scary to see blood while you're pregnant.

Here are some common causes of first-trimester bleeding:

  • Cervical infection, growths in the cervix or inflamed cervix
  • Ectopic pregnancy
  • Implantation bleeding, which typically happens about 2 weeks after conception
  • Miscarriage
  • Molar pregnancy

Causes of Second or Third-Trimester Bleeding

Here are some possible causes of bleeding experienced later during pregnancy:

A little bit of bleeding can also occur at the very end of pregnancy and serve as a sign that you are about to deliver. This blood is often mixed with mucus and called bloody show.

When to Contact Your Doctor

Once again, many women who experience some bleeding during pregnancy go on to have uneventful births and normal babies. However, bleeding during pregnancy should be treated as a pressing concern.

You must immediately contact your OB-GYN as soon as you notice any bleeding during pregnancy. Furthermore, you must tell your physician whether bleeding during pregnancy is accompanied by any other worrisome symptoms, such as cramping, fever, contractions, or chills.

Please remember that your physician is there to help you in a compassionate and comprehensive manner and must know about all the issues that you're experiencing. Sometimes bleeding during pregnancy can be life-threatening for the mother and the baby.

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2 Sources
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  1. Pathak N, Praveen M. Cyclical bleeding up to second trimester of pregnancy in bicornuate uterus: A case reportRes J Ob Gyn. 2010;3:5-7. doi:10.3923/rjog.2010.5.7

  2. American College of Obstetricians and Gynecologists. Bleeding during pregnancy. Updated February 2019.