This paper from the UK gives a detailed and thorough summary of a lot of the current knowledge about CHI. As well as the pathophysiology (the body processes when things go wrong), it covers many things that we already suspect – CHI is a rare condition (6 in 10,000 pregnancies) but that if you are diagnosed with it, the chances of it happening again are between 1 and 4 and the 100% and often ends with a pregnancy not resulting in a living child. They note that it seems to be an (inappropriate) immune response to the placenta and describe is plenty of detail how the immune response in pregnancy is complex and a balancing act between not rejecting the baby – who will have the father’s antigens (any foreign substance that elicits an immune response) – while simultaneously protecting the mother. They suggest that treatment avenues that suppress the immune response the way that immune responses need to be suppressed if someone receives a transplant could be a research route to take. They also discuss how there might be a way to test in advance whether the mother’s body is more or less likely to “reject” a specific fetus, the way they can test people due to have a specific organ transplant.