Baby Development 1st Trimester Highlights

A lot has happened in the past three months. Your baby is only 3 or 4 inches long, but already can open and close his fists and mouth. Fingernails and toenails are just beginning to develop. Already, your tiny baby has:

  • A brain, spinal cord, and flexible backbone
  • Lungs that are not fully developed
  • A heart that beats 120 to 160 beats per minute
  • All major organs, but not fully developed
  • A soft skeleton
  • Eyes with eyelids that stay closed
  • A nose, mouth, and chin
  • Distinct fingers and toes and tiny fingernails
  • Genitalia, not fully developed
  • Little teeth buds
WebMD Medical Reference Reviewed by Traci C. Johnson, MD on January 15, 2019



ACOG: "Your Pregnancy and Childbirth."

Moore: "The Developing Human."

Phillips, J. Pathology, October 2009.

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