Fetal Yawning May Signal Mild Stress, Study Finds
Even in the womb, fetuses yawn—a behavior observed as early as 11 weeks of gestation. New research published February 25, 2026, in PLOS One suggests that the frequency of these yawns may be linked to fetal well-being, potentially indicating mild stress in healthy fetuses.
What the Study Revealed
Researchers at the Università degli Studi di Ferrara in Italy, led by Damiano Menin, used ultrasound to observe 32 healthy fetuses between 23 and 31 weeks of gestation. Each fetus was monitored for approximately 22.5 minutes. The study found that, on average, fetuses yawned 3.63 times per hour, ranging from zero to six yawns during the observation period.
Notably, fetuses who yawned more frequently during the ultrasound observations were more likely to have a lower birth weight. While all the fetuses in the study were born healthy, lower birth weight can be an indicator of mild fetal distress.
Why Do Fetuses Yawn?
Yawning is a common behavior across many vertebrate species, but its purpose remains a mystery. In the case of fetuses, the act of yawning is particularly intriguing, as they are not breathing air. The researchers suggest that frequent yawning could be a sign of the fetus responding to some form of stress within the womb.
“We found that yawning frequencies in the womb are negatively related to birth weight, potentially indicating a stress-related response in healthy fetuses,” explained the study authors. “This suggests that even before birth, yawning may serve as an indicator of a fetus’s well-being.”
Limitations and Future Research
The researchers acknowledge that their study did not attempt to manipulate yawning behavior or record other physiological measures, such as fetal heart rate or maternal temperature, which could provide additional insights. The study only included healthy pregnancies, so the findings may not be generalizable to high-risk pregnancies.
Further research is needed to fully understand the causes and implications of fetal yawning. Investigating the relationship between yawning frequency and other indicators of fetal well-being could help refine our understanding of this intriguing behavior and potentially lead to improved prenatal care.
Source
Menin, D., Veronese, P., Gervasi, M. T., Oster, H., & Dondi, M. (2026). Fetal yawning and mouth openings: Frequency, developmental trends, and association with birth weight. PLOS One. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0341339