Guide to Being 15 Weeks Pregnant

What's Going On in Your Body

Length: About 4 inches. Weight: About 2.5 ounces. Lungs: Starting to develop.

Yes, this is a big week, with a tiny little body setting the stage for perhaps the greatest shock it will experience at birth: the first breath. He or she has started moving amniotic fluid through a primitive respiratory passageway, which triggers the development of the air sacs he or she will use when the environment switches from fluid to air.

Other big developments this week include:

  • Continued (or beginning) growth of lanugo, a fine coating of hair all over that acts as insulation until body fat starts to accumulate
  • Legs growing to a more proportional length (longer than the arms)
  • Continued growth in ability to move, with potential for swimming around and maybe thumb sucking
  • Development of pigment in hair follicle, and possible appearance of real scalp hair and eyebrows
  • Ability to sense light (through the eyelids -- they're not open yet)

A tiny heart is now pumping about 25 quarts of blood every day -- a pittance compared with the 300 gallons it'll be pumping at delivery, but still impressive for a 2.5-ounce being.

These stunning feats of new life are happening right there inside your growing abdomen -- which brings us to a second-trimester fact your partner might want to take special note of …