Development Update Into Second Trimester


Congratulations—you’ve made it through the first trimester! Your baby has come a long way in these first 13 weeks. Let’s take a look at the incredible amount of development that’s already taken place.

Weeks 5-10 (embryonic stage)

During these early weeks, your baby was called an embryo. The first microscopic stem cells began to multiply and develop, becoming all of the hundreds of different kinds of cells that will eventually make up your baby’s tiny body.

While your baby was busy taking shape, the placenta also formed, along with the umbilical cord that now carries nutrients and oxygen to your baby (and waste away from him or her). The amniotic sac developed, surrounding your baby with amniotic fluid that will protect him or her from injury, while helping to regulate body temperature. During this time, your baby’s organs and major body parts also began to form, including:

  • The heart (which has already begun to beat)
  • The brain, spinal cord and nervous system
  • The eyes, ears and facial features
  • Arms and legs
  • Tooth buds
  • Boy or girl parts
  • Muscles (and the first tiny movements)

Weeks 11-13

At this point, your baby is about one inch long, and is now called a fetus. Now is when growth and development come more quickly, and your baby will grow longer and heavier while the organs and other parts of the body continue to develop. The highlights of these last few weeks of the first trimester include:

  • Baby grows to about three inches long
  • The kidneys start to produce urine
  • Tiny fingernails and toenails form
  • Bones start to grow