Babies undergo a variety of changes throughout the nine months of development before birth. A baby's brain will also continue to expand and develop to allow for monumental changes, like the ability to feel changes in temperature. Here’s a look at how your baby begins to sense and regulate heat and cold temperatures.
Temperature and Neurological Development
The ability for a developing fetus to feel temperature comes from their nervous system. The receptive portion of sensory neurons, or thermo-receptors, becomes more advanced so they’re able to code changes in temperature. The receptors thought to respond to warmth are “unmyelinated C-fibers” -- these fibers reach the brain within a few seconds and have a low-conduction velocity. Conversely, cold triggers C-fibers and A-delta fibers send signals to the brain within a second.
Regulating Body Temperature
At the same time your baby begins sensing external temperatures, they also begin to regulate their own internal temperature, largely due to the hypothalamus in their brain. The hypothalamus acts as a control center -- think of it (in part) as the body's thermostat. It knows what temperature your baby's body should be and sends messages to keep it regulated.
Around the fifth month of pregnancy babies develop a fine, downy covering of hair called “lanugo.” This hair grows on the parts the body without a lot of fat. Lanugo not only helps insulate your baby and keeps them warm, it also helps regulate body temperature. At about 32 weeks, lanugo begins falling off -- around the time the brain is developed enough to take over regulation.
Temperature and Premature Babies
Since the development of temperature sensitivity occurs late in pregnancy, babies born prematurely will be less sensitive to temperature changes later in life -- research suggests this can happen to babies born 14-weeks early or before. Premature babies who undergo surgery show the least sensitivity to temperature changes.
Once born, premature babies tend to have greater difficulty keeping themselves warm -- because they don’t have the extra months to pack on the pounds. Low birth weight correlates to a tendency of coldness. However, even full term babies lose heat about four times faster than an adult.
Maternal Influence on Internal Conditions
Internal maternal temperature stays relatively constant, since you (as the mom) regulate your body temperature using your own hypothalamus. A trip outside in very hot or very cold weather shouldn’t have an effect on the baby, because maternal body temperature shouldn’t fluctuate wildly. Only in extreme circumstances, like hypothermia, where the mother's body temperature is altered significantly, will the baby notice a change.
