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How Big is a 17-Week-Old Fetus?

author image Annie Tumlin
Annie Tumlin is based in Overland Park, Kan., and has been writing since 2002. She contributes to various websites, including the blog for a fitness studio, specializing in parenting, pregnancy, health and wellness. Tumlin holds a Bachelor of Arts in education and English from Rockhurst University, and has worked in various education settings.
How Big is a 17-Week-Old Fetus?
Pregnant Photo Credit pojoslaw/iStock/Getty Images

The beginning of the second trimester brings many moms relief from morning sickness and the overall tired feelings of the first trimester. By week 17 baby is fully active inside the womb and the belly is starting to show proof of growing baby.

Baby is Getting Bigger

At 17 weeks, baby is already about 5 oz. and 5 inches long. The start of the second trimester gives baby a more human look as her body growth catches up with her head giving her normal proportions. Even though baby has only been developing for a little over four months, she can already swallow and practices tiny suckling motions with her mouth. Her fingertips are developing and soon fingerprints become apparent on her tiny fingers; she also practices breathing movements, although she won’t actually breathe oxygen through her lungs until birth. She swallows the amniotic fluid and relies on the strengthening umbilical cord for all of her nutrients and oxygen. Her bones are getting harder as they transfer from cartilage to bone, although they stay flexible to make it through the birth canal.

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Mom is Feeling Flutters

Mom's belly is starting to show and at 17 weeks mom may be able to feel the baby move, though some women may not feel the tiny fluttering for two or three more weeks. To many women, the intimate feelings of baby's movements give "proof" of the life inside them; up until seeing the protruding belly and feeling the fetal movements it is common to feel unconnected to the pregnancy.

Ultrasound Tell-All

Some moms are able to have their first ultrasound in the beginning of pregnancy to establish a due date, but for others the first ultrasound happens around 17 to 18 weeks. Parents are able to see their baby looking more like a human and doing things like holding her hands together and sucking her thumb. If baby is a boy his prostate has begun to develop, and the sex can be determined should the parents choose to see the surprise. At 17 weeks baby has the same heart rate she will at birth, about 140 to 150 beats per minute.

Weight Gain Woes

Many moms worry about their weight because the second trimester brings the normal 1-lb.-per-week gain. According to Heidi Murkoff in “What to Expect When You’re Expecting,” “dieting to lose or maintain weight is never appropriate during pregnancy, and it is an especially dangerous game during the second and third trimesters, when fetal growth is dramatically swift and significant.” It is normal to have gained almost 10 lbs. by the end of week 17 (3 to 5 lbs. in the first trimester and 4 to 5 lbs. from weeks 13 to 17.)

Enjoying the Honeymoon Phase of Pregnancy

By the second trimester women can enjoy their pregnancies more with the absence of morning sickness and tiredness and the addition of finally "feeling" pregnant through fetal movements and their growing belly. At 17 weeks mom may finally feel up to exercising. “Your Pregnancy Week by Week” remind parents that 17 weeks along is a nice "in between" phase to sit back and really enjoy pregnancy.

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