Does Pregnancy Affect Women's Voices?

From glowing skin to morning sickness, pregnancy can go hand-in-hand with a host of physiological changes. Now, a new study is suggesting that "having a bun in the oven" can temporarily cause a woman's voice to become deeper.

Led by researchers from the University of Sussex, the study found that the voices of new mothers are lower and more monotone more roughly 12 months after giving birth. Specifically, they claim that tones drop by two musical notes.

The “vocal masculinising" phenomenon

The study analysed voice recordings of natural, free speech sourced from 20 mothers, including a handful of celebrities. When comparing them to a control group, the team noted that the mean voice pitch of new mothers dropped by over 5%, the equivalent of around 1.3 semitones. Furthermore, the ability to reach high noted dropped by 2.2 semitones, which indicates that new mothers experience a significant decline in pitch variation.

“Our results demonstrate that pregnancy has a transient and perceptually salient masculinising effect on women’s voices,” comments the authors. “Previous research has shown that women’s voices can change with fertility, with pitch increasing around the time of ovulation each month, and decreasing following menopause."

For British singer-songwriter Adele, this “vocal masculinising” made it much easier to hit the hauntingly low notes made famous in her James Bond theme song, Skyfall. Actress Kristen Bell experienced a similar phenomenon, noting that after giving birth she had to re-record voice over work she did for the animated film Frozen as her vocal tones had considerably changed.

Hormones or hierarchy?

So what's behind the drop? Lead researcher Dr Kasia Pisanski muses that the change could be a biological indicator designed to help new mothers gain authority.

“This effect could also be behavioural. Research has already shown that people with low-pitched voices are typically judged to be more competent, mature, and dominant, so it could be that women are modulating their own voices to sound more authoritative, faced with the new challenges of parenting,” explains Pisanski.

Other theories suggest vocal masculinising could be spurred by hormones, with the team explaining that after pregnancy there's usually a sharp decline in the levels of key sex hormones. In turn, this could lower vocal fold dynamics.

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