Twins Development 1st Trimester Highlights

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

  • Brains, spinal cords, and flexible backbones
  • Lungs, but not fully developed
  • Hearts beating 120 to 160 beats per minute
  • All major organs, but not fully developed
  • Soft skeletons
  • Eyes with eyelids that stay closed
  • Noses, mouths, and chins
  • Distinct fingers and toes and tiny fingernails
  • Genitalia, but not fully developed
  • Little teeth buds
WebMD Medical Reference Reviewed by Nivin Todd, MD on January 16, 2019



ACOG: "Your Pregnancy and Childbirth."

Moore: "The Developing Human."

Phillips, J. Pathology, October 2009.

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