Week Twelve. Your baby is two-and-a-half inches long and may weigh up to half an ounce—really growing now. The external sex organs would be evident if you looked directly at the baby, but ultrasound viewing still isn’t quite precise enough for predictions at this stage. This is a fun time to watch the baby’s facial expressions and movement as this tiny human being delights in new-found mobility. Three-dimensional imaging has revealed that during the twelfth week babies appear to walk and leap in the womb.

Week Thirteen. Your baby is now two and two-thirds to three inches long from head to bottom. That is serious growth. Baby can hear and respond to sound, though the ear structures are still developing and maturing. Baby is completely formed now, but the organs are immature. So his or her life could not be sustained independently outside the womb’s protective environment.

Week Fourteen. Baby grows to four inches by this week and weighs one ounce. (That’s about what twelve pennies weigh.) This week marks the beginning of the second trimester. The placenta is now fully responsible for supplying the oxygen needs and all nutrients to the baby. Baby is breathing, moving, and doing other activities. External sex organs are sometimes visible by now with the ultrasound (though I like to wait a bit longer before making predictions).

Baby’s Weight

Sixteen weeks Baby weighs about one-half pound

Twenty weeks Baby weighs about three-quarters of a pound