Hearing in the Womb

Later in pregnancy, the fetus can distinguish different voices⁵ and different syllables, such as “Ba-Bi vs. Bi-Ba.”⁶ At birth, the baby can easily recognize his mother’s voice, her native language, and music that he has heard in the last ten weeks of pregnancy. ^{7 8 9}

Sounds are quieter and lower in pitch inside the uterus. The mother’s heartbeat, bloodflow and digestive system all create sounds for the fetus’s developing ears to hear. The lowest pitches in the mother’s voice reach the fetal ears quite easily.¹⁰ The relative lack of high-pitch sounds interspersed with a rich variety of low-pitched sounds allows neurons in the fetal brain to correctly wire to the cells in the cochlea so that hair cells in the cochlea can detect pitches 1/30th of the difference between notes played by two adjacent piano keys. Most of this tuning occurs between 28 weeks gestation and the first few months after birth.¹¹ Interestingly, when researchers recorded brain activity from fetuses every two weeks from 28 weeks gestation through the first few weeks after birth, they observed an electrical pattern often seen when adults distinguish different pitches, even in the youngest fetuses.¹²

While in the womb, the fetus gets lots of exposure to his mother’s voice, which resonates throughout her body and easily transmits to the fetal ears. Using fMRI, scientists discovered that by 34 weeks, the fetus recognizes his mother’s voice — his brain responds differently to his mother’s voice than an unfamiliar female voice.¹⁹ Similarly, at birth, newborns prefer their mother’s voice over a female stranger’s voice,²⁰ stories read in their native language compared to a foreign language,²¹ and a story read by the mother for the last six weeks of pregnancy compared to a new story.²² These examples show that newborns remember sounds from in the womb. But how much exposure have they had to their father’s voice?

A newborn baby prefers her mother’s voice over her father’s voice. A father’s voice typically reaches the womb more faintly than a mother’s because it must pass through the mother’s body and is heard less often during the day. Even so, late in pregnancy fetuses can recognize both parents’ voices. In one study, 38-week fetuses showed heart-rate responses to both their mother’s and father’s voices, although the response was stronger when the mother spoke aloud in real time. When recordings equalized the volume of both voices, fetal responses were similar. After birth, newborns prefer their mother’s voice but can still recognize their father’s voice and distinguish it from other male voices.^{24 25} Surprisingly, even though babies as late as four months old can recognize their father’s voice, they still show no preference for his voice compared to a male stranger.²⁶

Nevertheless, fathers still play an irreplaceable role in connecting with their children both inside and outside the womb. Fathers and newborns have been shown to time their gazes and vocalizations such that they create a ‘conversation’ as early as 2 to 4 days old.²⁷ Furthermore, premature infants who listened to male or female voices singing in the hospital were healthier—their eating improved, they gained more weight and went home sooner.²⁸ Also, when mothers and fathers spoke directly to their premature infants, those infants had better periods of quiet alertness followed by deeper sleep.²⁹