Any parent with two or more children knows that babies are different at birth and often those differences persist as the baby develops. Developmentalists refer to individual differences that are constitutional (i.e., present at birth but not necessarily expressed until later in infancy) as “temperament”. Of course, many circumstances, including how children are raised and the environment that they are raised in, can amplify or constrain a child’s individual tendencies. At the core of individual differences are two basic elements: the speed and intensity in reacting to events or stimuli, and the recovery after the response. Differences in temperament are understood to originate from variation in the central nervous system which develops and differentiates during gestation.

Differences among newborns do not originate during passage through the birth canal; late term fetuses express virtually all of the same behaviors as do newborn infants. So differences among individuals must begin during fetal development as the nervous system matures into characteristic patterns of response. Despite general acceptance that this is the case, there is scant evidence to back it up. In part this is due to the inaccessibility of the fetus, it is no easy feat to study something that cannot be directly viewed or handled. We set about collecting data on the two most conspicuous and measurable features of fetal functioning – heart rate and motor activity – in over 300 fetuses during the third trimester. In order to evaluate fetal reactivity and recovery, we relied on the known effect that stimulating pregnant women has on the fetus. Women took a cognitive challenge, the Stroop Color Word Task, activating their own physiological systems, which, in turn, generated changes in fetal heart rate and motor activity. Ten or so years after they were born, we interviewed and gave mothers questionnaires about their child’s behavior and personality.

We admit this was a bit of a long shot. The fetus and child inhabit vastly different worlds. The late term fetus is upside down, knees to ears, in an obscure fluid-filled environment; the 10 year old child is fully sentiment and self-aware as she goes about her business. Nonetheless, slower and less variable fetal heart rate at 32 weeks gestation along with less motor activity predicted higher levels of shyness and fearful temperament in childhood. In addition, fetuses that showed greater rebound in their heart rate response to the maternal challenge were more likely to have fewer behavioral difficulties than those that recovered less completely. The common denominator between the two is likely related to a child’s ability to self-regulate.

While this is the most comprehensive study to date to reveal that fundamental elements of individual differences originate before birth, by no means does it imply that a child’s fate is fixed at birth nor that predictions can be made for individual children. The amount of shared correspondence between fetus and child was only about 6% to 10%.  While this seems small, it is not that far off from studies that seek to establish consistency in traits from one period of childhood to another. Considering the limits of measurement in the fetal period and variation in context between the fetus and child, we suspect the findings underestimate the true predictability from the prenatal period. One final thought – the prenatal period is not monolithic and it is important to note that the findings are generated from the last trimester of pregnancy as the fetus nears delivery and the nervous system is mature enough to express individual patterns of behavior. Despite these caveats, the period before birth remains an intriguing yet enigmatic frontier of developmental inquiry.

Learn more by reading, Predicting child temperament and behavior from the fetus, published on August 2018 from Development and Psychopathology.

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