Fetal Development

There are many reasons why understanding how far you are in your pregnancy (gestational age) is important. Knowing the gestational age will help you to know how your baby is developing and growing at this stage of your pregnancy. This information is often key to helping you make healthy choices - both physically and emotionally - for your pregnancy and life.

If the gestational age is:

First Trimester (0-13 Weeks after LMP)

Everything necessary for the fetus to grow into an adult human is formed within the first trimester of your pregnancy.

By the end of the 1st Trimester the fetus' main job will be to grow and mature until it reaches around 40 weeks.

Second Trimester (12-24 Weeks after LMP)

If you are already in your 2nd trimester, everything that your baby needs to become an adult person has already been developed. It will continue to grow and mature inside your uterus until it is ready to be born. Here is what has formed already:

In the 2nd trimester these systems will continue to mature and grow into place as your baby also increases in length and weight. In addition, the following will take place:

Third Trimester (25-40 Weeks after LMP)

If you are already in your third trimester, you should know that everything that your baby needs to become an adult person has already been developed. At this point your baby will continue to mature and grow in length and weight.

Here is what has formed already:


1. Pennsylvania Department of Health. "Abortion Making A Decision." Commonwealth of Pennsylvania.

2. American Pregnancy Association. First Trimester. Available at: http://americanpregnancy.org/duringpregnancy/fetaldevelopment1.htm. Accessed October 8, 2013.

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