A baby born at or near full term naturally stays curled up in the fetal position, tucked in like a little ball. The arms and legs are bent and the back curved. When placed on her back, her knees come up and her hands are near her face.
When placed on her stomach, she lies curled up, her bum in the air with her knees and toes touching the mattress.
Whether the baby is on her back or on her stomach, her arms and legs are free to move at will.
What to aim for:
- Arms and legs symmetrically placed
- Movements smooth, organized, coordinated
- Position calming and relaxing
- Development optimal
How does that work?
We all have muscle tone, which means that we hold our muscles in a certain way, even without effort; this is called “muscle tone at rest”. Muscle tone helps us maintain posture and joint alignment, whether we move or sit still. In the infant, muscle tone develops gradually. Muscle tone is controlled by the brain and nervous system, which grow and form connections throughout pregnancy and particularly in the last trimester and the months following a full-term birth. By 18-24 months’ corrected age, the child walks and proper muscle tone is pretty much established.
You can observe muscle tone development in the postures your child assumes, on his back, on his stomach, when he learns to hold his head, as well as in the movement milestones he can achieve, particularly in the first year.
There are several stages of muscle tone development:
- Progressive strength in flexion (bending) of the arms and legs at rest – 24 to 40 weeks’ gestation. Maximum flexion can be observed in the legs at 32 weeks’ gestation and in the arms at 40 weeks.
- Gradual loss of muscle flexion at rest – arms open at 2-4 months’ corrected age, legs at 5-7 months. Relaxation of arm flexion tone allows the baby to hold objects, like a toy or a bottle, at a certain distance from the body. It also allows the baby to bear weight on his forearms as he lifts his head and chest off the mattress when on his stomach. Relaxation of leg flexion tone allows the baby to sit without falling backward and, eventually, to stand.
- Maximum flexibility – 8-15 months’ corrected age. The baby is very flexible and loves bringing the feet up to the mouth. Though some flexibility will be lost as he grows, the child will retain excellent flexibility nonetheless. How much depends on genetic factors and physical activity.
Fit in flexion
In a baby born full-term, the space within the mother’s womb gets tighter as the pregnancy progresses in the third trimester and the baby grows ever larger. For the baby to fit in the small space, he has to flex his limbs and curl into a ball. Not surprising that maximum flexion is observed at 32-40 weeks.
The preterm baby, on the other hand, may not have had enough time to grow and experience such space constraints. Therefore, flexion may not be as developed as in a full-term baby and the baby may have a tendency to sprawl straight out.
Though this explanation is somewhat simplistic, it helps us understand the importance of keeping the preterm baby within certain positioning to allow proper muscle development and alignment. These influence everything from posture to the development of fine and gross motor skills.
Français