Fetal Development Weeks 14 Through 17

See what's happening with your baby in the fourth month of your pregnancy.

four months pregnant
Photo: AngelaLuchianiuc/Shutterstock.com

Week 14

Pat yourself and on the back -- and give your baby a pat, too! You've both reached the second trimester -- the so-called "honeymoon phase" of pregnancy. Your baby is growing by leaps and bounds, and so is your uterus, which is why you may be sporting a noticeable belly bump at this point, or at least finding that your clothes are tighter. At this point in your baby's development, expressions begin to flicker across her face -- little winces and grimaces. But this is simply a flexing of muscles, not an indication of mood. Mouth-muscle flexing is especially important: these sucking motions are your baby's most basic reflex and will enable her to eat.

Baby now weighs about an ounce, but by the end of this trimester at 28 weeks, it will top two pounds. It will from about three inches to a foot in length. (Keep in mind that all babies grow at different rates -- our figures are averages).

Week 15

Will your baby be bald as a cueball, or emerge with a mop of dark hair? That's now being decided, as hair sprouts on the scalp. Hair also appears as eyebrows and on other parts of the baby's body, too. Baby's legs, back, and belly are covered by a downy fuzz called "lanugo," most of which will disappear before birth. Is this hair just a holdover from our furry caveman days, or does it serve some protective purpose in the womb? Scientists don't yet know for sure.

Mind-blowing fact: Like a tiny sea creature, your baby is able to breathe "underwater." Beginning anywhere from ten to fifteen weeks, the fetus inhales and exhales small amounts of amniotic fluid. This helps the lungs to develop and grow.

Week 16

At somewhere around three inches long, your baby is just about big enough these days to make herself known to the outside world. Any day now -- usually between weeks 16 and 20 -- she'll be bumping up against the walls of the amniotic sac, producing those little flutters and tickles that you'll feel as "quickening." An ultrasound might be able detect your baby's sexual organs, and an external monitor could pick up the thumps of her tiny heart, which by now is pumping 25 quarts of blood a day to every corner of her growing body.

In both face and body, this baby looks more human. Her head and neck are held straighter now, and her proportions are becoming more "normal." Her eyes have now moved from the sides to the center of the face. Eyelids are shut firmly, and won't open again until the seventh month of pregnancy.

Week 17

Vocabulary word of the week: meconium. This black goo, your baby's first feces, is the product of cell loss, digestive secretion and swallowed amniotic fluid. As pregnancy progresses, meconium begins to accumulate in the bowels. It will appear -- usually after birth, though occasionally in utero -- as baby's first poop!

Baby is firmly attached to the placenta via the umbilical cord, which is growing thicker and stronger, thanks to the blood and nutrients constantly rushing through it. His skeleton is transforming from soft cartilage to bone. These bones remain flexible though, so that this precious package can pass more easily through the birth canal.

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Reviewed 2008

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