Recurrent miscarriage is a blight on a couple. There is only so many times a person can cope with being told it is “bad luck” or “the odds are really in your favour next time”. Undoubtedly this may be true for many couples, and a number of women are labelled as suffering from recurrent pregnancy loss or miscarriage when in fact the lottery which is early pregnancy has not been in their favour. However there certainly does seem to be a group where there is a real problem. Looking at their reproductive history is often illuminating. Getting pregnant is easy – in fact if anything they are super fertile with conception times of one to two months. The result is pregnancy after pregnancy in quick succession – but all ending in miscarriage. This appears to be a high risk group where something different is going on.
There have been many hypotheses to explain apparent recurrent miscarriage from disorders of blood clotting to thyroid disease and NK cells.
Professor Jan Brosens of Warwick University has a different hypothesis. He believes the problem relates to defective decidualisation. This is the process whereby the cells in the endometrium change (differentiate) from ones that are called stromal into “decidual” cells. If decidualisation takes place properly Brosens believes the endometrium has the ability to recognise defective embryos and in effect reject them. In a sense the normally decimalised endometrium acts as a natural quality control measure. Conversely a failure of the process of decidualisation means quality control is impaired and is associated with early placental failure. This also means the implantation window will be longer which might explain the super fertility seen in women with recurrent miscarriage.
The idea of miscarriage being associated with a prolonged implantation window is not new. In 1999 Wilcox published a seminal paper in the New England Journal of Medicine on the same subject – where he looked at the implantation window by examining the LH surge in relation to the first appearance of hCG in serum.
The decidualisation hypothesis is attractive as is pulls together a number of strands. It is unifying in that it explains increased miscarriage, super fertility, sub fertility and the possible development of late obstetric complications due to impaired placentation. It also means that a tendency to miscarry may be transient and the implantation window may correct itself – or indeed be amenable to intervention to treat the disorder. Professor Brosens (pictured left) work is innovative and it will be fascinating to see how this area of research develops.