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Second Trimester Infant Development
A look at how your baby changes from week 14 to week 25.
by: Dr. Peter Doubilet and Dr. Carol Benson
Second Trimester Development
- At 15 weeks, your baby can make facial expressions and may even suck her thumb.
- By 17 weeks, an ultrasound should be able to show you the sex of your baby.
- By 19 weeks, your baby will be able to hear your voice if you read her a story or sing a song.
- Your baby will measure a little over a foot in length and will weigh more than one pound by end of the second trimester.
ften referred to as "the honeymoon phase," the second trimester lies between the first, in which women are often plagued by morning sickness, and the third, in which moms are often carrying so much extra weight that they're ready for the pregnancy to be over. And, when it comes to ultrasounds, the second trimester is the most exciting time for parents. The baby's face, limbs, and internal organs are now large enough to see in exquisite detail. And, if your baby cooperates during your ultrasound, you may even be able to determine its sex.
Weeks 14 to 16
In the first two weeks of the second trimester, your baby is about four inches long, or the length of a bell pepper (measured from the top of the head to the bottom of the rump). The body is now growing faster than the head so the fetus is becoming more proportional to what your baby will look like once she is born. Your little one is gaining weight quickly and is now about two or three ounces.
During this stage, the baby is still small enough that ultrasound can show a full body view on the screen, but big enough that details of the face are quite apparent. Although you may not be able to make out her expressions, she can now squint, frown and grimace. You may even see her sucking her thumb.
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| 15-week 2D ultrasound image of baby lying on her back and looking upward. |
Weeks 16 to 20
This is the time when doctors usually perform an ultrasound to make sure all your baby's body parts are developing normally. It's also the ultrasound where, if your baby is positioned correctly, you will find out whether you're having a boy or a girl. The sonogram at this stage typically includes pictures of the baby's face, extremities and internal organs, such as the brain, heart and kidneys.
Your baby now weighs about half a pound and is five to six inches–the length of a banana. She is too long for her whole body to fit on the ultrasound screen, so images during this period will show individual parts. By about 19 weeks, your baby's hearing is improving and she will start to detect external sounds and will even be able to hear your voice.
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| 19-week 3D ultrasound of face and upper body | 19-week 2D ultrasound of arm and hand |
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.
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25-week 3D ultrasound of baby's face |
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25-week ultrasound of baby's brain |
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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.
