Fetuses yawn before they are born. The frequency with which they yawn may reveal information about their health. This is according to a University of Ferrara study, which found that between the 23rd and 31st weeks of gestation, fetuses who yawn more frequently have a little lower birth weight, despite remaining within standard norms and being born healthy. The research, which was published in the international scientific journal PLOS ONE, was conducted by Damiano Menin and Marco Dondi of the Department of Humanities at the University of Ferrara, in collaboration with the University of Padua and New York University. Through 4D ultrasound, the researchers conducted an analysis of 32 healthy fetuses, analyzing the recordings frame by frame using a validated method that enables them to differentiate between genuine yawns and simple mouth openings. This is an important methodological consideration, as confusion between these activities has previously resulted in inaccurate estimations. The average frequency observed was roughly 3.6 yawns per hour (median about 2), with no significant changes with gestational age. The significant discovery, however, is the correlation with birth weight: a minor decrease in birth weight was observed as yawn frequency increased; however, this did not suggest any pathological condition. "We found a negative relationship between fetal yawn frequency and birth weight", the researchers explain. "This finding could reflect a stress-related response even in healthy fetuses, suggesting that yawning is involved in physiological regulation mechanisms even before birth". The authors note that the study did not show a cause-and-effect link and that fetal yawning cannot be utilized as a diagnostic tool. All of the girls and boys in the research were born full-term and in good health. In addition to potential future clinical developments, this study adds to the scholarly discussion about the functions of yawning, a behavior found in all vertebrates, implying that some regulatory mechanisms seen after birth are already functioning during intrauterine life.