Week 12 of Pregnancy: What's Going On Inside

Topic Overview

Congratulations, you've made it through your first trimester! You can now hear your baby's heartbeat with a Doppler heart monitor. That can be very exciting.

Inside your uterus, an important organ called the placenta has formed. The placenta's main job is to give your baby oxygen and nutrients through the umbilical cord.

Wondering what your baby looks like now? As you enter the fourth month of pregnancy, your baby is about the size of a plum. Average baby length is 61 mm (2.4 in.).

How your baby is changing

Here are some of the important facts and developments around 12 weeks.

• When you are 10 weeks pregnant, your embryo has nearly all of the body structures that an adult has. The brain is now more complex. After this point, we call this tiny being a fetus.
• This month, the tiny fetus starts moving the head and jaw, grasping, moving the tongue, and stretching. Eyelids are covering the eyes, and fingernails are starting to grow.
• At the end of this month, the fetus starts a big weight gain.