Many parents talk to and even sing to their babies while they're still in the womb. They might not know how much the baby can really hear, but it can be used as a way of bonding with their unborn bub.
Now, a new study has shown that babies may actually be able to hear from as early as 16 weeks – 10 weeks earlier than was commonly thought. And a new video even shows babies' unusual reactions to hearing music in the womb.
Researchers at the Institut Marques in Barcelona used two types of speakers – headphones held to women's stomachs, and a special speaker inserted intravaginally – and ultrasounds to track the babies' movement when they were played Bach's Partita in A Minor.
Before the music started, researchers noted that around 45 per cent of the babies made random head and limb movements, 30 per cent moved their mouth or tongue, and 10 per cent stuck their tongues out.
When the music was played to the mothers' bumps, there was little reaction from the babies.
But when the sound was played through the vaginal device, 87 per cent of the babies reacted by moving their head and limbs more. And half the babies in the study performed an unusual move, opening their mouth very wide and sticking their tongue out as far as they could. The movements stopped when the music stopped.
The study was performed on babies from 14 to 39 weeks, but the first response was noticed with babies at 16 weeks, the researchers said, "with statistically significant variations throughout the pregnancy".
"The further on the mother is in the pregnancy, the more striking the facial movements," the research, published in the journal Ultrasound, says.
"Response is different for each foetus, with different response levels each time the music is played."
Dr Marisa Lopez-Teijon, who led the study, said the video shows babies moving their mouths "as if they were trying to speak or sing". This shows that the communication part of the brain is working even before the baby is born, she pointed out.
But there are further implications, too: researchers say their method could help start to diagnose deafness early, even before birth.