In the womb 7
These 40 images are some of the earliest ever taken of a fetus in the womb. This is an embryo of just 6 weeks. The fetus is on the left and the yolk sac still bigger than the fetus is on the right. Here an embryo of 8 weeks just over an inch long makes its first movements.
这40张图是最早拍摄的一批子宫里胚胎的图像。这是一张六周胚胎的图片，胎儿在左边，比胎儿还要大的卵黄囊在右边。这是一个八周的胚胎，长度刚刚超过一英寸，正在开始它的第一次运动。
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 amniotic(羊膜的) sac(囊). If two eggs are released and fertilized at the same time, the twins are non-identical or fraternal(兄弟的) 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 separated placentas, so blood flow to each twin is carefully monitored throughout the pregnancy. Other than the slightly early birth, complications are minimal.
除了能检查孩子是否健康，扫瞄还能让你确定到底怀了一个、两个甚至更多的孩子。多胞胎有家族遗传史。如果你母亲的家族有生异卵双胞胎的传统，那么你也非常有可能生一对双胞胎。同卵双胞胎是由一个受精卵分裂为两个细胞而形成的双胞胎。这种双胞胎两人拥有相同的DNA，并使用同一个胎盘，而且在子宫里有1%的时间使用同一个羊膜囊。如果母亲同时产生两个卵子并且它们同时受精，这样的双胞胎就是异卵双胞胎，或者说双胞胎两个人是兄弟、兄妹或姐妹关系，他们没有相同的DNA。这种双胞胎在子宫里分别生活在各自的羊膜囊里，并且有各自独立的胎盘，所以每个胎儿的血液循环在整个怀孕期间都必须被严密监视。除非是早产，一般来说胎儿出现并发症的可能性是极小的。
Even though she won’t be able to walk until she’s around a year old, the building blocks to her first steps are present after just 11 weeks in the womb. These 4D scans show a 11- and 12-week-old fetuses kicking and pushing out their legs in what’s known as the stepping reflex(跨步反射). A reflex action is a preprogrammed biological impulse. When her feet touch the base of the uterus, the nerve system triggers an automatic muscle reaction in the legs.
虽然婴儿要到一岁左右才会走路，但是让她迈出第一步的准备工作在11周的时候就开始了。4D扫瞄显示11-12周的胎儿已经会踢腿，这被称为跨步反射。反射运动是一种先天的生理现象。当胎儿的脚碰到子宫时，神经系统会使腿部肌肉自动产生条件反射。
At this age, there are so much space in the uterus, the fetus bounces and leaps around, using the walls of the womb like a trampoline(蹦床). The ability to walk is an important survival skill. And the more the fetus moves, the stronger the reflex grows. This stepping reflex can be clearly be seen in a newborns when their feet dangle(摇摆) above the ground.
这个时期的子宫里空间很大，所以胎儿就到处乱碰乱撞，它把子宫壁当作了游戏的蹦床。走路是生存的一种重要技能。胎儿运动得越多，它的跨步反射能力就发展得越好。跨步反射在新生儿身上可以很清晰地看出来，他们的脚总是在不停地摆动着。
The period from 6 to 11 weeks has seen the most dramatic transformation of the entire pregnancy with the fetus undergoing the metamorphosis(变形) and growing nearly five times bigger in a frantic 5-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 the human baby have formed, and it’s still less than 3 inches long.
6-11周是整个怀孕期间变化最大的时期，子宫里完成了从受精卵到胎儿的变形，胎儿在五周的时间里疯狂地长到了原来的五倍大。胎儿身上产生了超过200种不同形态的细胞，肌肉和神经系统也在剧烈变化。她已经有了一个肝，两个肾，一个跟一粒米差不多大的胃。人的所有器官都已经成形，但是胎儿仍然还不到三英寸长。
After 12 weeks, the fetus enters the second trimester, the middle three months of pregnancy. Although she is still no bigger than a fist, she’s much less delicate and there is less risk of a miscarriage(流产). 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% of fertilized eggs survive all the way through pregnancy.
12周以后，胎儿就进入了第二个三月期，也就是怀孕中间的三个月。虽然她还没有一个拳头大，但是已经没有那么脆弱，母亲发生流产的可能性已经很小。流产大部分发生在怀孕的头三个月里，这个时候新的胚胎正在形成。免疫系统的不平衡、沉重的压力、或者母亲根本就想要一个男孩都可能导致流产的发生。只有50%的受精卵能够存活下来并走完整个怀孕旅程。
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