Kicking in utero may be related to brain development.
Feeling a baby kick is a normal part of being pregnant. A new study, however, sheds more insight into why a fetus kicks — and how it helps them develop.
The researchers examined the sleep patterns of 19 newborns between 31 and 42 weeks. The infants in the study were already born, but some were born prematurely.
They noted the infants “corrected gestational age,” which is the accurate age of a baby from conception regardless of when they are born. For instance, an infant who was 1-week old but born at 35 weeks would be 36 weeks old. Infants are considered full term anywhere from 37 to 42 weeks.
Researchers looked at the brainwaves that fetuses produce when they kick during rapid eye movement (REM) sleep.
When the fetus moves its right hand, for example, it produces brainwaves immediately afterwards in the part of the left-brain hemisphere that processes touch for the right hand.
The brainwaves are extremely fast in premature babies. (In the case of this study, they noted that premature babies who were already born would typically still be in the womb when these fast brainwaves occur.)
By the time the babies are a few weeks old, the fast brainwaves naturally disappear.
Fetal kicks in the third trimester help the infant develop brain areas linked to sensory input. They are also tied to helping the baby form a sense of their own body, the scientists say.
"Spontaneous movement and consequent feedback from the environment during the early developmental period are known to be necessary for proper brain mapping in animals, such as rats. Here we showed that this may be true in humans too," Lorenzo Fabrizi, PhD, the lead researcher said in a statement.
“For example, it is already routine for infants to be 'nested' in their cots. This allows them to 'feel' a surface when their limbs kick, as if they were still inside the womb,” she said. The study supports the notion that sleep should be protected and interruptions minimized, as the findings show how important movement is during fetal and premature newborn sleep.
Kimberley Whitehead, a research associate in the Division of Biosciences, University College London said the findings could help hospitals provide an optimal environment for infants born prematurely.
Whitehead told Healthline that animal experiments have demonstrated that spontaneous movement and feedback from the environment during the early developmental period are necessary for proper brain mapping. They think it is similar in humans, although that has not been proven yet, she said.
The team’s finding about infant brain activity changes with movement could impact future studies.
“We were surprised that although the movement-evoked fast brainwaves disappear a few weeks after the average time of birth, movement continues to trigger slow brainwaves,” she said. This draws on her team’s previous
Whitehead said they plan to continue studying movement in babies, but they are also focused on how aspects of brain development are processed, such as touch and painful stimuli (as with a blood test, for example).
“I think this research is intriguing,” Dr. Scott Sullivan, a professor and director of maternal-fetal medicine at the Medical University of South Carolina in Charleston. Not only does it define critical brain development that occurs in late gestation, but it also shows that active sleep movements contribute strongly to cortical mapping. The research also reinforces the importance of sleep for newborns and suggests that preterm babies, even those near to term, might have these cycles interrupted or delayed.
“More research is needed [to determine] how nursery care may need to be changed to not interrupt these important developmental steps,” Sullivan said.
The medical community already knows a good deal about the quality, frequency, and perceptibility of fetal movements, said Dr. Amber Samuel, medical director, maternal-fetal medicine at the Obstetrix Medical Group of Houston. Sporadic movements at about 9 or 10 weeks become more organized in the second trimester. Mothers can feel a fetus kick as early as 15 weeks.
As the brain develops, the fetus kicks and responds to their own brain activity, as well as to changes in maternal movement, sound, temperature, and other stimuli.
“The perception of fetal movement changes in the third trimester to body rolling more often than distinctive kicks but all fetal movement is reassuring even if the quality evolves,” Samuel said.
Fetal kicking serves several purposes, added Sullivan. The first is that it gives muscles and limbs exercise. It also shows response to stimuli and, as the current study suggests, helps the brain make connections for spatial sense.
Doctors still aren’t sure what the changes in frequency of movement means. Many fetuses have longer than usual periods of inactivity. In some cases of stillborn infants or in utero death, they can come as a result of decreased movement. Still, the medical community is not sure based on those perceptions which babies may be more at risk than others, Samuel said.
One commonly used “kick count” system suggests that mothers should feel 10 movements every 2 hours.
“No type of system has been more useful than others for predicting if there may be a problem developing. Additionally, most research does not support that kick counts can prevent stillbirth,” she said.
“All healthy babies move but some moms of healthy babies may not feel it as much as others,” she added.
That’s why Samuel generally tells patients they should be aware of what is normal for their baby including type and frequency of movement and the typical time of day.
“Many women will not feel distinct movements in the course of a busy afternoon, so I recommend monitoring your baby during a time when you have known he or she to be active and when there are other [no] distractions, like in the evening,” she said. “If movement becomes markedly less or absent, patients should inform their healthcare provider for further steps.”
Researchers found that fetal kicks in the third trimester may help the infant develop brain areas linked to sensory input. They are also tied to helping the baby form a sense of their own body, the scientists say.