DC 2007-04-30, In The Womb 子宫日记 13

In normal circumstances, there is no need for the scanning probe to go anywhere near the ear, but if the baby becomes at all unhappy she can easily wriggle away from the sound. Just as in this 4D scan, doctors have observed fetus's grimace and frown as they manipulate the fetus through the mother's abdomen, all part of the delicate expansion of the senses. During the final trimester, the fetus prepares for life outside the womb away from her comforting cocoon and its built-in life support. Many of the crucial tricks and skills she needs to survive on the outside are innate reflexes that she develops inside the womb.

From the 26th week, babies spend about 90 percent of their time sleeping, and when they sleep nothing can wake them. For the other 10 percent of the time they are awake and alert ready for whatever might happen next. They may react to sudden sounds with the startle reflex flinging their arms and legs out to the side. The startle reflex is thought to have originated at a time when we were more at a risk of being eaten. A sudden noise or touch from a predator triggers the reflex and causes the arms to fling out to the side in what may be an attempted self-preservation. This may not be so relevant to our lives today, but other reflexes are crucial to survival after birth.

In this 4D image, the fetus swallows amniotic fluid. During this trimester, she will swallow a pint of fluid every day. By drinking, the fetus helps maintain the liquid balance in the womb. It also helps her digestive system develop properly. But from the moment she is born and the cord is cut she needs to have perfected the art of taking food from her mouth to her stomach.

Along with swallowing one of the most important reflexes to perfect before birth is sucking. Anything vaguely nipple-size that comes close to her mouth triggers her attempts at the sucking reflex. This fetus, 25 weeks old, first sucked its thumb at about 11 weeks at which time it may have already begun to develop a lifelong preference for one hand or the other. Ultrasound scans have shown that as soon as thumb sucking begins, a fetus tends to show a clear preference for either the left or right thumb. This left or right handedness which stays with it for life develops in the womb rather than during early childhood as was previously thought.

At 26th weeks, the fetus measures almost 10 inches from head to toe. She is growing fast and as she moves through the third trimester towards birth, the fetus will triple her weight and double her length. The brain and nervous system will continue to grow dramatically. And soon the fetus will create something even more remarkable. At 26th weeks, the baby's parents may enjoy a pleasant surprise. Now it's possible to hear the fetal heartbeat just by putting an ear to the mother's abdomen. ("Is she kicking?")