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Babies' Development During the Second Trimester

August 14, 2013 by HealthyFamilies BC

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The second trimester is a time of rapid growth for your baby (called a fetus).  

Most of the brain's development begins now and will continue after your baby's birth.

The lungs, heart and blood systems are also developing during this three-month period, to the point where the fetus will be capable of living outside your body after about the 24th week.

You'll also be able to see your baby during your first ultrasound. This typically happens around 18 to 20 weeks. The ultrasound will check the baby’s growth and position and provide an estimated due date. You will also likely feel movement, usually after 19 weeks if this is your first baby. Some women feel movement earlier or later. It's called quickening, and is often described as bubbling or fluttering.

Here’s a more detailed look at development in the second trimester:


16 weeks: 16 cm (6 1/2 in.) 100 g (4 oz.)



Baby’s face looks more human, the head has hair, the ears stand out, and your voice can be heard.



17-20 weeks: 25 cm (10 in.) 300 g (10 oz.)

The developing baby begins to store some of your antibodies. This slowly increases until birth.

Eyebrows and eyelashes appear. A fine downy hair (lanugo) appears all over the baby’s body and may be present at birth.

The skin is thin, shiny, and covered with a creamy protective coating called vernix. Oil glands appear. The baby’s legs lengthen and move well. Teeth develop - enamel and dentine are being formed (this can begin as early as 14 weeks.)

By the end of the fifth month, baby is about half the length of a newborn. Meconium (baby’s first poop) begins to appear in the intestines.


24-26 weeks: 30 cm (12 in.) 600 g (1 1/3 lb.)

 Sweat glands form. The baby has a lean body with red and wrinkled skin. Early breathing movements begin.

A substance called surfactant is formed in the lungs to help them expand normally after the baby is born. The baby’s outline may be felt through your abdomen. The eyes may be open now.



Ultrasounds can check your baby’s size and position and estimate your due date. An ultrasound uses reflected sound waves to produce a picture of your fetus, the placenta, and the amniotic fluid. Fetal ultrasound is a safe way to check for problems and get information about your fetus, such as its size and position. It does not use X rays or other types of radiation that may harm your fetus. For more information about ultrasounds during pregnancy, visit the HealthLink BC File Fetal Ultrasound: Test Overview.

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