Busy little baby! What’s happening during the first trimester

The tissues that will form the heart begin to beat. The heartbeat can be detected!

Busy little baby! What’s happening during the first trimester
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We know that it feels like you’re super hard at work as a pregnant mama, dodging waves of morning sickness and extreme exhaustion. But it’s fun to think about how much your little one is doing during this time as well. From growing fingernails to lengthening his legs, your fetus is starting to look more like a teeny tiny person! Good work, mini human!


We consulted the American College of Obstetricians and Gynecologists to share a rundown of all that’s happening during baby’s development at this time.

What happens during weeks 1 to 4 of pregnancy?

  • The dividing fertilized egg moves down the fallopian tube toward the uterus.
  • About five days after fertilization, the cluster of dividing cells enters the uterus.
  • About eight to nine days after fertilization, the cluster of cells (now called a blastocyst) attaches to the lining of the uterus.

What happens during weeks 5 to 8 of pregnancy?

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  • The placenta begins to form.
  • The brain and spinal cord begin to form.
  • The tissues that will form the heart begin to beat. The heartbeat can be detected during an ultrasound exam at about six weeks of pregnancy.
  • Buds for limbs appear with paddle-like hands and feet.
  • The eyes, ears and nose begin to develop. Eyelids form, but remain closed.
  • The genitals begin to develop.
  • By the end of the eighth week, all major organs and body systems have begun to develop.

What happens during weeks 9 to 12 of pregnancy?

  • Buds for future teeth appear.
  • Fingers and toes start to form. Soft nails begin to form.
  • Bones and muscles begin to grow.
  • The intestines begin to form.
  • The backbone is soft and can flex.
  • The skin is thin and transparent.
  • The hands are more developed than the feet.
  • The arms are longer than the legs.

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