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Babies' Development During the Second Trimester


pregnant woman and man in field outdoors



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:

Time: 16 weeks





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


16 weeks


Time: 17-20 weeks




17 weeks: The developing baby begins to store some of your antibodies. A vaginal birth also helps your baby's immune system develop as important bacteria from your gut is transferred to your baby.

20 weeks: 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.


20 weeks


Time: 24-26 weeks


24 weeks: Sweat glands form. The baby has a lean body with red 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.

26 weeks: 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. For more information about ultrasounds during pregnancy, visit the Health Link BC File> Fetal Ultrasound: Test Overview.

Last Updated: January 18, 2018