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Why are some women more prone to miscarriages than others? It's a question that has baffled doctors and medical experts for decades.
But a new study may shed some light on the problem. Research suggests that "super-fertile" women may be more likely to have multiple miscarriages, possibly because their uteruses are more accepting of implantation, whether the embryo is healthy or not.
"This is important as - for the last 60 years - the whole field believed that miscarriage is the consequence of maternal rejection of the fetus because of immunological differences," Jan Brosens of the University of Warwick told LiveScience. Brosens is the co-author of the study, which was recently published in the journal PLoS ONE.
Instead, the new research points to a different explanation.
"Recurrent miscarriages can now be seen not as failure to carry a pregnancy, but perhaps as failure to prevent one, in other words super-fertility, but with distressing consequences," wrote Nick Macklon, co-author of the study and a professor of obstetrics and gynecology at the University of Southampton in the U.K.
In the U.S. alone, 1 in 10 pregnancies end in miscarriages, and 1 to 2% of couples have more than three miscarriages in a row, which is known as recurrent miscarriages. In most of those situations, doctors have difficulty pinpointing a problem. What this new study suggests is that a woman’s uterus could potentially allow unhealthy embryos to implant - instead of rejecting what won’t survive and only allowing healthy embryos to implant.
The sample for the study involved six women who had suffered with recurring miscarriages and compared them to six women with normal fertility. The researchers placed high- and low-quality embryos on channels in between strips of uterus cells of the two groups of women. The cells of the women with normal fertility rejected the low-quality embryos while the cells of the women with “super-receptive” cells accepted both high- and low-quality embryos.
Researchers believe that their findings may help women to understand miscarriage in a new way - and ultimately pave the way for new treatment.
"Many sufferers of recurrent miscarriage feel that they are failing as mothers, because they seem to reject lots of pregnancies," wrote Macklon. "In fact, the opposite may be the case: They are super-fertile, allowing embryos which would normally be allowed to implant and survive long enough to show up as a pregnancy, before miscarrying."