Top parenting stories this week

• 1.  Why Babies Smile
• 2.  Changing from Two Naps to One
• 3.  What Happens to Your Body After Childbirth
• 4.  Lower Back Pain after Baby
• 5.  When to Start Sleep Training

Second Trimester Infant Development

Weeks 20 to 25

Your baby is now swallowing more–excellent practice for her digestive system once she is born. And that's not all she's trying out. You will feel so many kicks and punches at this stage that you may feel as though you have a mini acrobat tumbling inside of you. Late in the second trimester, your baby will reach two size milestones. She will measure a little over a foot in length (the size of a cob of corn) and will weigh one pound before week 25 is over.

Developmentally, you will also be able to see her lips, nose and eyes in more detail. You can also see the brain's cerebral hemispheres, which are responsible for thinking, feeling, and controlling movement, as well as the cerebellum, which is in charge of muscle coordination.

As the baby progresses through your pregnancy, you can watch the brain grow and change in contour from smooth early in the second trimester, to wavy in the late second trimester (as seen below), to highly furrowed in the third trimester. The infoldings during this brain development provide enough surface area to hold the full complement of human brain cells after birth.

	25-week 3D ultrasound of baby's face
	25-week ultrasound of baby's brain
	A detailed look at baby's brain development by 25 weeks.

Meet our experts:

Peter Doubilet, MD, PhD and Carol B. Benson, MD are professors of radiology at Harvard Medical School and obstetrical ultrasound specialists at the Brigham & Women's Hospital in Boston. You can learn much more about pregnancy through the "eyes" of ultrasound in Peter and Carol's new book Your Developing Baby (McGraw-Hill, 2008). It offers an illuminating "tour" of life in-utero using remarkable 2D and 3D ultrasound images, original explanatory diagrams and reader-friendly prose. For more information, visit www.YourDevelopingBaby.com.