(1) DeCasper, A. J., & Fifer, W. P. (1980). Of human bonding: Newborns prefer their mothers' voices. Science, 208(4448), 1174-1176.

The most compelling evidence for the efficacy of talking to the womb comes from neonatal studies. DeCasper and Fifer’s seminal 1980 study demonstrated that newborns prefer their mother’s voice over a stranger’s, as measured by non-nutritive sucking responses. A follow-up study (DeCasper & Spence, 1986) found that infants exposed to a specific, repeatedly recited passage of text ( The Cat in the Hat ) during the last six weeks of pregnancy subsequently preferred that passage over a novel text.

Research has shown that babies in the womb are capable of detecting and responding to external stimuli, including sound, light, and even taste. By around 24 weeks of gestation, a baby's auditory system is developed enough to detect sounds outside the womb. This includes the sound of their mother's voice, which is transmitted through the bloodstream and tissues of the body.