DC 2007-04-18, In The Womb 子宫日记 8

In most miscarriages, which occur in the first trimester, the mother is unaware of what has happened and may mistake her miscarriage for a heavy period. Initially, as they develop, male and female fetuses have identical genitals. Both sexes have a protuberance which for boys will become a penis and for girls a clitoris.

At 12 weeks, the only difference is that they stick out at different angles. Looking at an ultrasound, an expert might guess the sex of the baby based on this angle. But it will be a few more weeks before there is a clear difference between male and female genitals. But in each case the sex organs are already hard at work. For a male, the testicles are producing testosterone and the ovaries of a baby girl are already busy making her own supply of eggs.

After 4 months, the fetus is still running on reflexes but big changes are taking place. Her nervous system is up and running and her movements are increasingly being controlled by her brain. At 5 and a half inches long, she is much more mobile now, muscles are flexing, fingers and toes are separated and defined, and her bones are hardening.

Hands develop before the feet, which could be because they are going to be used first once the baby is born, or it could be, because the hands, being important sensory organs, develop at the same time as all the other sensors are beginning to form.

The eyes have grown closer together, giving the fetus a more human look. The central nervous system extends its connections from the brain to most parts of the body, allowing the brain to gradually establish total control. The heart, for instance, is no long beating spontaneously and spasmodically. Instead, the brain regulates the muscles and keeps them pumping blood at a steady 140 to 150 beats per minute.

Using a Doppler probe, it's now possible to hear what a baby's heart sounds like.

"It's 146 beats per minute in the heart, you see, which is just the right pace."

As the nervous system extends throughout the fetus, so too does her capacity to respond to stimulus. She is becoming sensitive to touch and if prodded through the mother's abdomen, she is likely to squirm.

From 4 months on, the fetus makes a lot of intricate movements. She can bend, flex and twist her extremities, her fingers, wrists, legs and toes. More incredible she is already beginning to develop an awareness of the space around her. It's called proprioception, the unconscious sense of her body's place in space that helps her interact with her environment.

This 4-D scan shows actual footage of a fetus reaching up to touch her head. In these computer-generated images, the movements have been taking directly from observations of the 4-D scans. Sensors give constant feedback to the brain and the movement can then be refined and gradually perfected.

words and phrases:

squirm: To twist about in a wriggling, snakelike motion; writhe. 蠕动，如同蛇一样弯弯曲曲地蠕动；扭动

flex : [1]To contract (a muscle, for example). [2]To bend (a joint).