Super-fertility may explain miscarriages
Scientists say women who have multiple miscarriages may be too fertile, with their wombs too good at letting embryos implant – even those of inferior quality
24th August 2012 - According to a study published in the journal PLoS ONE, a UK-Dutch team has found evidence that in women with recurrent miscarriages, their wombs are more likely to accept embryos, even if they are of low quality.
Losing three or more pregnancies in a row affects around one in 100 women in the UK. Foetal, uterine and other abnormalities are indicated in a number of these women, but having recurrent miscarriages remains largely unexplained in more than 50% of cases.
The scientists considered increasing evidence that recurrent miscarriages occur in some women when 'super-receptive' endometrium (the lining of the womb) allows low-quality embryos to implant, establishing a 'clinical' pregnancy, only to be miscarried.
The study compared six women with normal fertility with six women who have experienced recurrent miscarriages. It found that in women with recurrent miscarriages, the human endometrial stromal cells (H-EnSCs) in the womb were less effective at telling apart low-quality and high-quality human embryos than in women with normal fertility. These cells more readily migrated towards low-quality embryos in women with recurrent miscarriages than in women with normal fertility.
In laboratory conditions, the scientists created cell-free migration zones where they studied the effect of the presence of a high-quality embryo, a low-quality embryo or a trophoblast cell-lined spheroid on the migratory activity of the H-ENSCs.
Without a spheroid or embryo, the migration of H-EnSCs was similar, whether from a fertile woman or one with recurrent miscarriage. When a low-quality embryo was present in the zone, the migration of H-EnSCs of the fertile women was inhibited, but that was not the case in women with recurrent miscarriages - for them, the H-EnSCs were the same between high- and low-quality embryos, and their migration was even greater than in fertile women when a spheroid was present.
Dr Siobhan Quenby, from the Royal College Obstetricians and Gynaecologists, says in a statement: "This theory is really quite attractive... It's a really important paper that will change the way we think about implantation. It had been thought that rejecting normal embryos resulted in miscarriage, but what explains the clinical syndrome is that everything is being let in."
Research should now, according to Dr Quenby, look into whether women could be tested for super-receptive wombs and if there is a way to alter their receptiveness to low-quality embryos.