Human uterus seems to be highly selective when it comes to accepting embryos, for a new study has shown that women with less 'fussy' uteruses may be at higher risk of miscarriage.
For years, faulty embryos or problems such as abnormal clotting or immune responses have been blamed for miscarriages.
Jan Brosens at Imperial College London wanted to know if another process was involved.
He had noted that many women who had repeated miscarriages claimed to have conceived incredibly quickly.
"Each one of their pregnancies was conceived within one or two months of trying," New Scientist quoted Brosens as saying.
Also, some studies have hinted that embryos implanting outside the normal window of uterine receptivity were more likely to miscarry.
For further investigation, Brosens and his colleagues took cells from the uteruses of women who had undergone miscarriages and ones who hadn't.
They measured the expression of a key regulator of uterine receptivity called PROK1 and levels of prolactin, a marker of decidualisation - the monthly process by which the uterus prepares to receive an embryo.
Decidualisation involves a thickening of the uterine wall and the growth of new blood vessels.
Expression of PROK1 was higher in the women who had miscarried than in those who hadn't and this was maintained for longer, suggesting that their implantation window lasts longer.
These women also produced far less prolactin, a sign that their cells don't decidualise properly.
Further studies indicated that this impaired decidualisation interfered with the signalling between the embryo and the uterus at the time of implantation.
The researchers concluded that these uteruses are less picky, allowing abnormal embryos to implant, which later spontaneously abort.
The study has been published in the journal PLoS One.