pregnancy loss and olfaction

Human reproduction is remarkably inefficient; nearly 70% of human conceptions do not survive to live birth. Spontaneous fetal chromosome aneuploidy is the most common cause for spontaneous loss, particularly in the first trimester of pregnancy. Presumably, pregnant women don't sense the chromosome integrity of a conceptus. 

Thus, it is interesting to read that among the fraction of conceptions that come to the attention of the woman, there could be an environmental mechanism in operation in some cases:

"Overall, these experiments provide compelling evidence that women who have experienced unexplained repeated pregnancy loss perceive socially important odors in a different way, and that this is associated with specific changes in brain structure and function. However, this latest work does not reveal causal links between olfaction and the condition, and further research is needed to establish whether these differences in perception arise as a consequence of experiencing multiple miscarriages or whether they are present beforehand."

https://elifesciences.org/articles/62534?utm_source=content_alert&utm_medium=email&utm_content=fulltext&utm_campaign=30-September-20-elife-alert