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An interesting question that was asked during a lecture about human reproduction: what is the biological mechanism behind some pregnant women getting monthly spotting that they mistake for a regular period? I've found articles and research papers about bleeding during zygote implantation, ectopic pregnancies and problems with the placement of the placenta, but nothing regarding menses-like bleeding during otherwise unproblematic pregnancies.

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Related: How common is it to be pregnant with periods? – Cornelius Jul 29 '14 at 11:54

Here are some causes of bleeding during pregnancy:

  • early pregnancy (first trimester):
    • implantation bleeding [1]
    • infection [1]
    • after intercourse [1]
    • miscarriage [2]
    • ectopic pregnancy [2]
    • cervical changes [3]
  • second part of pregnancy:
    • abruptio placentae [1, 2]
    • placenta previa [1, 2]
    • miscarriage [2]
    • vasa previa [2]
    • preterm labour [1]


  1. American Pregnancy Association. Bleeding During Pregnancy. Available from (accessed 29.07.2014)
  2. U.S. National Library of Medicine. A.D.A.M. Medical Encyclopedia. Vaginal bleeding in pregnancy. Available from (accessed 29.07.2014)
  3. WebMD, LLC. Bleeding During Pregnancy. Available from (accessed 29.07.2014)
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