cycle - How common is it to be pregnant with periods?

As you may know, some women claim that they have their period while they are pregnant. In the arab world they call it "Deer pregnancy", since when the deer gets pregnant, it still gets its' monthly cycle.

Their doctors do confirm that. The appearance of such: The bleeding comes at the times when the period is expected, but is usually without pain, or smell, and lasts for less days. It is also of different color. But many women (and doctors) still call it a period.

(Although we all know, a real period is impossible biologically).

How common is that?

This is, I think, different from implantation bleeding, since it mostly continues to three months and after that.

Answer

But many women (and doctors) still call it a period.

It is not a period:

Pregnant women can have some light irregular bleeding during pregnancy, but it should not be like a “normal” period. Some women can confuse this for their period because often it can come right around the time she was expecting her normal period. [...] It should not be enough bleeding to fill pads or tampons over a few days [1].

It is quite common in the first trimester:

Vaginal bleeding during pregnancy can occur frequently in the first trimester of pregnancy and may not be a sign of problems. But bleeding that occurs in the second and third trimester of pregnancy can often be a sign of a possible complication [2].

It happens to about 25 % of pregnant women:

Up to 1 in 4 women have vaginal bleeding at some time during their pregnancy. Bleeding is more commonin the first 3 months (first trimester), especially with twins [3].

Repetitive bleeding is associated with preterm birth:

Bleeding of multiple episodes, on multiple days, and with more total blood loss was associated with an approximate twofold increased risk of earlier preterm birth, PPROM (preterm premature rupture of the membranes), and preterm labor. In contrast, bleeding in the second trimester only, of a single episode, on a single day, and with less total blood loss was not associated with any category of preterm birth [4].

---

References:

1. American Pregnancy Association. Am I Pregnant: FAQs On Early Pregnancy. Available from http://americanpregnancy.org/gettingpregnant/pregnancyfaq.htm (accessed 29.07.2014)


2. American Pregnancy Association. Bleeding During Pregnancy. Available from http://americanpregnancy.org/pregnancycomplications/bleedingduringpreg.html (accessed 29.07.2014)



3. U.S. National Library of Medicine. A.D.A.M. Medical Encyclopedia. Vaginal bleeding in pregnancy. Available from http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0003748/ (accessed 29.07.2014)


4. Yang J, Hartmann KE, Savitz DA, Herring AH, Dole N, Olshan AF, Thorp JM. Vaginal bleeding during pregnancy and preterm birth. Am. J. Epidemiol. 2004 Jul 15;160(2):118-25. doi: 10.1093/aje/kwh180. PubMed PMID: 15234932.