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1 June 2018, 11:23 | Updated: 1 June 2018, 11:26
New mothers’ voices become temporarily deeper and more monotone for around a year after having their first child, scientists have claimed.
Researchers from the University of Sussex found the voices of new mothers can drop by more than a whole tone after pregnancy.
But the team claims the ‘masculinising effect’ does not last forever. Voices tend to revert to their previous pitch after one year.
They speculated the change could be hormonal, or an attempt by mothers to sound more authoritative towards their children.
Head researcher Dr Kasia Pisanski, of the University of Sussex’s School of Psychology, said: “Our results show that, despite some singers noticing that their voices get lower while pregnant, the big drop actually happens after they give birth.”
The researchers added: “Our results demonstrate that pregnancy has a transient and perceptually salient masculinising effect on women’s voices.”
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The study looked at 20 mothers, including singers, actresses, celebrities and journalists, and compared them to a control group.
They analysed archive interview footage from five years before and after pregnancy, and found women’s average voice pitch had dropped by over five per cent – the equivalent of 1.3 semitones.
The highest pitch in the group dropped by an average of 2.2 semitones, and there was less variation in the frequency of their voice.
“One possible explanation is that this is caused by hormone changes after childbirth,” said Pisanski.
“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.
“We know that after pregnancy, there’s a sharp drop in the levels of key sex hormones, and that this could influence vocal fold dynamics and vocal control.
“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.”