Your developing baby – week 12

by Kaiser Permanente |
Fetus at week 12, illustration

At 12 weeks, your baby is about 3 inches long and weighs nearly 1 ounce. The baby is now about the size of a lime.

The baby's:

  • Brain and spinal cord are developing quickly.
  • Sex organs are developing, although they can’t yet be seen.
  • Fingernails and toenails are starting to form.
  • Vocal cords are forming.
  • Kidneys can function on their own now, which means your baby can urinate.

Your baby can squint, frown, open and shut their mouth, turn their head, make a fist, and kick.

Amniotic fluid (the bag of waters) surrounds and cushions your baby, allowing them to move around easily. However, you probably still cannot feel the baby moving.

It’s possible to hear your baby’s heartbeat. We use highly sensitive Doppler ultrasound to hear the heartbeat. Just like you, your baby’s heart rate is faster when they move and slower when resting.

This article has been created by a national group of Kaiser Permanente ob-gyns, certified nurse-midwives, pediatricians, lactation consultants and other specialists who came together to provide you with the best pregnancy, birth, postpartum, and newborn information.

Some of the content is used and adapted with permission of The Permanente Medical Group.