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Baby -
Development
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Pregnancy Trimesters.Need more info on pregnancy trimesters, I know my developing baby is going through lots of changes. Can you explain some of them to me?
Your baby grows and changes from a small group of cells to a fully developed baby ready to begin life. Changes are easier to discuss if we look at them in each trimester.
What is a trimester?
Your pregnancy is divided into three trimesters, each about 13 weeks long.
How does my baby change during the 1st trimester?
This trimester is the one of greatest change for a developing fetus. In the first 13 weeks of development, your baby grows from a collection of cells the size of the head of a pin to a fetus the size of a softball. Organs begin developing, and your baby begins to look more normal. How does my baby change during the 2nd trimester?
At the beginning of the 2nd trimester (14th week), your baby weighs less than 1 ounce (28g) and is only about 4 inches (10cm) long. By the end of this trimester, your baby is almost 9 inches (22cm) long and weighs close to 1-1/2 pounds (0.7kg).
How does my baby change during the 3rd trimester?
Your baby weighs about 1-1/2 pounds (0.7kg) at the beginning of this trimester (27th week), and its crown-to-rump length is under 9 inches (22cm). When it is delivered, your baby weighs close to 7-1/2 pounds (3.4kg) and is about 21 inches (53cm) long.
What is the difference between an embryo and a fetus?
The designation between "embryo" and "fetus" is somewhat arbitrary. During the first 8 weeks of development (10 weeks of gestation), the developing baby is called an embryo. From 8 weeks of development until delivery it is called a fetus.
I read recently that the baby doesn't change very much after about the 12th week of pregnancy. What does this mean?
Very few, if any, structures in the fetus are formed after the 12th week of pregnancy. This means your baby forms all of its major organ systems by the end of the 1st trimester. However, these structures continue to grow and to develop until your baby is born.
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