Women who repeatedly reject pregnancies may be 'too good' at carrying, research indicates.
Recurrent miscarriage [RM], defined as three or more consecutive miscarriages, affects between one and two percent of couples trying to conceive. In more than 50 percent of cases, the causes of RM are unknown.
Professor Nick Macklon, of the University Hospital Southampton, who led the UK-Dutch collaborative study, said: 'We have discovered that [the causes of RM] may not be because [women] cannot carry; it is because they may simply be super-fertile, as they allow embryos which would not normally survive to implant'. Implantation is the name for the process where an embryo attaches to the lining of the uterus, shortly after conception.
The study, published in the journal PLoS ONE, looked at the endometrial stromal cells (H-EnSCs) of women with a history of RM. H-EnSCs line the uterus and are actively involved in the process of embryo implantation and may play a 'quality control' function.
In women unaffected by RM, H-EnSCs were found to regulate their behaviour in response to the quality of embryo presented. They grew towards high-quality embryos, but did not when confronted by a low-quality embryo, thereby ensuring only viable embryos progressed to pregnancy. In contrast, these cells failed to discern between high- and low-quality embryos in women with a history of RM.
The authors suggest that in RM this failure of H-EnSC quality control allows the implantation of poor quality embryos, leading to pregnancy and, ultimately, miscarriage as fetal development fails.
Professor Macklon said these results offer women 'a clearer understanding of the causes [of RM], they are not too bad at carrying but perhaps too good'.
Currently, no treatment options are available to women who experience RM, but Professor Macklon described these findings as a 'significant moment for sufferers'.
Dr Siobhan Quenby, from the Royal College Obstetricians and Gynaecologists, who was not involved in the study, agreed. She told BBC News: 'This theory is really quite attractive. It is lovely. It's a really important paper that will change the way we think about implantation'.
The mechanisms underlying the 'quality control' sensor remain poorly understood, and are expected to be the focus of future research.