Week 12 of Pregnancy: What's Going On Inside

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By week 12, you can now hear a fetus's heartbeat with a Doppler heart monitor.

Wondering what a fetus looks like at 12 weeks? It is now about the size of a lime.

How a fetus is changing

Here are some important changes that happen around this time.

  • By 10 weeks of pregnancy, an embryo has nearly all of the body structures that adults have. Its brain is now more complex. After this point, we call it a fetus.
  • During this month, the fetus's limbs, hands, and head start to move. Eyelids cover their eyes, and their fingernails are starting to grow.
  • At the end of this month, fetuses start a big weight gain.


Current as of: July 10, 2023

Author: Healthwise Staff
Clinical Review Board
All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.

The Health Encyclopedia contains general health information. Not all treatments or services described are covered benefits for Kaiser Permanente members or offered as services by Kaiser Permanente. For a list of covered benefits, please refer to your Evidence of Coverage or Summary Plan Description. For recommended treatments, please consult with your health care provider.