The uterus is undisputedly the ultimate environment for the development and nurturing of a fetus. The sensory systems develop throughout pregnancy and affect the brain’s development.
Fetal sensory development
Your baby begins to develop on a sensory level from the moment of conception. The first sense to develop is the sense of touch, emerging at 3 weeks gestation – before you knew you were pregnant. By the twelfth week, your baby can feel and responds to touch on his entire body, with the exception of the top of his head, which remains insensitive until birth.
The auditory system is completely intact by 20 weeks gestation but it is a few weeks before the nerves conducting sound are functional. At 23 weeks your baby can respond to loud noises and may jerk or even begin to hiccup after hearing a loud sound.
Taste buds emerge at 8 weeks and by 13-15 weeks your baby has taste buds similar to adults’. Anything you eat can flavour the amniotic fluid. While we are not exactly sure when the baby starts to perceive taste, we do know that a baby born prematurely (33 weeks) sucks harder at sweetened nipples and when saccharine is injected into the amniotic fluid in the third trimester babies suck faster.
Smell develops alongside the sense of taste. Since smells are essentially chemicals that are found to be present in amitotic fluid, it stands to reason that your baby can smell in utero as the chemicals pass from the amniotic fluid onto the smell receptors in the nasal cavity. The nasal cavity is protected by a plug of tissue until 28 weeks, but thereafter your baby will smell and respond to scents.
Your baby’s tiny eyelids open at 26 weeks and at 6 months we know that babies can see light in utero. At 32 weeks gestation your baby can track a bright torchlight shone and moved across your pregnant belly.
The sense of movement and gravity from the balance (vestibular) system in the ears develops very early and begins to function at five months gestation. Like the sense of hearing and touch, the sense of movement is relatively advanced at birth.
The world of the womb
Knowing that the sensory systems perceive the intrauterine world by the second and third trimesters, we may wonder what the womb world is like on a sensory level.
The womb world is devoid of light touch - deep pressure touch and the sense of warmth are greatest inputs to the sense of touch. By the third trimester, the elastic uterus provides constant, deep pressure, like an all-day hug or massage. This tight hug keeps your baby curled up, with pressure on his back and his hands towards the midline. In this position, your baby can suck his hands and his immature reflexes, which are starting to emerge in utero are contained so that he feels secure. The temperature in the womb is always perfect, a temperature we call neutral warmth. Threatening touch, such as pain, high or low temperatures and tickle are completely absent during gestation.
In the womb, the overwhelming sounds (about 85 decibels) are the background sounds of your body. Your baby hears the gushes of amniotic fluid and blood flowing in the veins and of course your heartbeat and digestion. These background noises contribute to the constant white noise he hears. The consistent sound of the heartbeat is a particularly soothing sound and babies who are played a beat at the pace of the average heartbeat (72 beats per minute) fall asleep easier and cry half a much after birth. Sounds from the outside world are subdued (55 decibels) but the clearest sound he hears is your voice as it is carried not only outside the body but also through your bones in the form of vibrations. Dad’s voice is the second most familiar sound to your baby and it is nice to know that within hours of birth your baby will recognize Dad by his voice.
Because all tastes you experiences pass into the amniotic fluid, your baby is prepared for the flavours your family eats even while in utero. The preference for sweet tastes is hardwired and babies prefer sweet flavours, swallowing amniotic more vigorously after you eat something sweet.
Even though your baby is interested in and tracks a bright light, the reality is that he is rarely exposed to bright lights and there is very little visual stimulation in utero. In general the womb world is visually muted and often it’s quite dark. There are no bright colours or contrasting shapes in utero on which your baby can hone his developing visual skills. For this reason the visual system is relatively immature at birth.
In utero your baby is buoyed by amniotic fluid and whirls freely in a contained liquid bubble. Since water decreases the weight of an object by 50 times, your baby has the wonderful sensation of being 1/50th lighter than on earth. He is lulled by the constant rocking and swaying motion of this gravity-reduced world, gently rocked to sleep. When the lulling movement stops – such as when you rest or lie down, your little one may become wakeful and busy. During the third trimester, your baby’s vestibular system has matured sufficiently to sense gravity and to turn to the appropriate ‘head down’ position in preparation for birth.
The fourth trimester
By understanding the world of the womb, you can make your little one’s transition to the real world smoother.
By Meg Faure
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