Women who have suffered unexplained repeated pregnancy loss (uRPL) have altered perceptions and brain responses to male body odors, in comparison to those with no history of uRPL, suggests a new study published today in eLife.
The results could lead to urgently needed answers for many women who experience repeat miscarriage with no clear underlying explanation.
Around 50% of human conceptions and 15% of human pregnancies result in miscarriage, but only a limited number of these can be explained. Body odour has been linked to many aspects of healthy human reproduction - such as synchrony of menstruation between women who live together, and the influence of body odors of breast-feeding women on the timing of ovulation and menstruation in others.
"Given that sense of smell is associated with human reproduction, we hypothesised that it may also be related to disorders of human reproduction," explains lead author Liron Rozenkrantz, who was a graduate student at the Azrieli National Institute for Human Brain Imaging and Research, and the Weizmann Institute of Science, Israel, and is now a Postdoctoral Fellow at the Massachusetts Institute of Technology (MIT), Cambridge, US.
"We set out to test the hypothesis that perception of smell - known as olfaction - is altered in unexplained pregnancy loss, specifically the smell of body odours."
The team started by testing a key olfactory function important in reproduction: the ability to identify mates by smell. They offered 33 women with uRPL and the same number of women with no history of uRPL (controls) three body odor sniff jars, containing body odor from their spouse, a non-spouse male and one with no odor.
They found that the women with a history of uRPL were twice as likely to correctly identify their spouse than the control women.
To see whether this was because the women with a history of uRPL had a better sense of smell, the team compared their ability to smell a range of different odors, such as peanuts and soap. The women with experience of uRPL were also better at discriminating between the smells, but only marginally.
The researchers next asked whether it was the characteristics of the men's body odors that made the women who have had uRPL better at identifying their spouse by smell.
They asked 36 women (18 who have experienced uRPL) to rate men's body odors based on intensity, pleasantness, sexual attraction and fertility. Based on these criteria, the uRPL group rated non-spouse body odors lower when compared with the control group.
To look at how these perceptions might be controlled, the team used MRI scans to look at brain structure and function. They found that women with a history of uRPL had smaller olfactory bulbs, which was surprising given their apparent greater ability to perceive and discriminate between different smells.
When they measured brain activity while the women watched an emotional film clip, with or without the subliminal presence of a non-spouse male body odor, they found a remarkable response in the hypothalamus region: while body odor increased the hypothalamus activity in women with history of uRPL, it decreased this activity in the control group.
We have found that women who experience unexplained pregnancy loss are much more likely to recognise their spouse by smell and rate men's body odour differently than other women."
Noam Sobel, Study Senior Author and Professor in Neurobiology, Azrieli National Institute for Human Brain Imaging and Research, Weizmann Institute of Science
"We have also found differences in structural and functional brain patterns, which have not been previously associated with unexplained repeat pregnancy loss. We hope our findings will help direct further thinking and research on this condition, which is currently not well understood or managed."
Rozenkrantz, L., et al. (2020) Unexplained repeated pregnancy loss is associated with altered perceptual and brain responses to men’s body-odor. eLife. doi.org/10.7554/eLife.55305.