Pregnancy Odor Reveals Unborn Baby's Sex

It’s long been suspected that males of many species, including humans, can sniff out whether a female is pregnant, and now new research suggests that some — if not all — female primates release a natural “pregnancy perfume” that males can probably detect.

What’s more, such scents appear to broadcast whether the mom-to-be is carrying a boy or a girl.

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The study, published in the journal Biology Letters, focused on lemurs as a model for primates. It presents the first direct evidence in any animal species that a pregnant mother’s scent differs depending on the sex of her baby.

The scent signatures “may help guide social interactions, potentially promoting mother–infant recognition, reducing intragroup conflict” or sort out paternity, wrote authors Jeremy Crawford and Christine Drea.

The latter presents a loaded scenario, as it could be that males can sense — even before the birth — whether they fathered the baby.

The researchers additionally suspect that odors advertising fetal sex may help dads and moms prepare for what’s to come.

Crawford, from the University of California, Berkeley, and Drea, from Duke University, used cotton swabs to collect scent secretions from the genital regions of 12 female ringtailed lemurs at the Duke Lemur Center in Durham, N.C., before and during pregnancy.

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The scientists next used chemical analysis to identify the hundreds of ingredients that make up each female’s scent change during pregnancy. A surprising finding from this is that expectant lemur moms give off simpler scents that contain fewer odor compounds compared with their pre-pregnancy bouquet. The change is more pronounced when the moms are carrying boys, Drea said.

She and Crawford found that the patterns correlate with changes in blood hormone levels.

“The difference in hormone profiles between pregnant lemurs carrying sons and those carrying daughters is dramatic,” she said in a press release.

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“It could be that producing these compounds uses resources that are directed elsewhere when they’re pregnant, especially if it’s more energetically costly for a female to have a male pregnancy than a female pregnancy,” she added.

Presumably, a male’s ability to detect pregnancy — and his possible connection — is particularly important for sexually promiscuous species. Lemurs and most other primates fall into that category. Humans do too.

Lemurs are not regarded as being the best scent-detectors, so it could also be that the release of the odors and detection of them are quite common throughout the animal kingdom.