DC 2007-04-16, In The Womb 子宫日记 7

These 4D images are some of the earliest ever taken of a fetus in the womb. This is an embryo of just six weeks. The fetus is on the left and the yolk sac still bigger than the fetus is on the right. Here an embryo of eight weeks just over an inch long makes its first movements.

As well as checking the health of the baby, this scan gives the first opportunity to determine if you are pregnant with one baby or two or more. Multiple births run in families. If your mother's family has a history of non-identical twins, then you are far more likely to have twins yourself. Identical twins are formed when an egg splits in two. The twins will share identical DNA and could even share the same placenta, but only 1% of the time will they share an amniotic sac. If two eggs are released and fertilized at the same time, the twins are non-identical or fraternal and don't share identical DNA. In this case the twins are separated in the womb with each living in its own amniotic sac.

They also have separate placentas, so blood flow to each twin is carefully monitored throughout pregnancy. Other than a slightly early birth, complications are minimal.

Even though she won't be able to walk until she is around a year old, the building blocks to her first steps are present after just 11 weeks in the womb. These 4D scans show 11- and 12-week-old fetuses kicking and pushing out their legs in what's known as the stepping reflex. A reflex action is a preprogrammed biological impulse. When her feet touch the base of the uterus, the nervous system triggers an automatic muscle reaction in the legs.

At this age, there is so much space in the uterus. The fetus bounces and leaps around, using the walls of the womb like a trampoline. The ability to walk is an important survival skill. And the more the fetus moves, the stronger the reflex grows. This stepping reflex can clearly be seen in newborns when their feet dangle above the ground.

The period from 6 to 11 weeks has seen the most dramatic transformation of the entire pregnancy with the fetus undergoing the metamorphosis and growing nearly five times bigger in a frantic five-week burst. Over 200 types of cells have been made. Muscles and nerves are twitching. There is a liver, two kidneys, and a stomach no bigger than a grain of rice. All the organs of a human baby have formed and it's still less than three inches long.

After twelve weeks, the fetus enters the second trimester, the middle three months of pregnancy. Although she is still no bigger than a fist, she is much less delicate and there is less risk of a miscarriage. Miscarriages are most common in the first three months when new cells are developing. An imbalance in the immune system, stress, or if the mother has previously given birth to a boy could all increase the risk. Only 50 percent of fertilized eggs survive all the way through pregnancy.

words and phrases:

trampoline: 蹦床
dangle : To hang loosely and swing or sway to and fro
miscarriage: 流产