Second Trimester Fetal Development

second trimester fetal development

You’ve made it through the first trimester. Congrats, mama! The second trimester is generally considered to include weeks 13 to 26 of your pregnancy, and this is the favorite trimester of many women. The morning sickness will start to (hopefully) dissipate soon, you’ll likely get a return of energy, and as your belly starts making its appearance, the pregnancy will finally feel a bit more “real” when people comment on it. It’s also a time when many women finally feel relaxed enough to make the big announcement to others that they’re expecting. A lot happens this trimester, and not just on the outside!

By now, your baby has gone from a ball of cells to a fetus with organs, muscles, and limbs! At the start of your second trimester, the fetus is only about 3 inches long. This trimester is full of developments, and this is the time when you’ll be able to finally feel those first fetal movements, as well, called “quickening.”

Weeks 13 through 16:
By week 14, the sex of the baby will start to become obvious. Either ovarian follicles begin forming, or the prostate develops. By the following week, the skeleton begins forming bones, which you’ll be able to see at a future ultrasound. The fetus has begun to swallow some amniotic fluid and practice sucking movements, and fingerprints are beginning to form on those tiny fingers!

Weeks 17 through 21:
Around weeks 17-20, you might be starting to feel some flutters. It can be hard to know if this is fetal movement, since it can feel like popcorn popping, rubber bands snapping from the inside, or even gas bubbles. The eyebrows and eyelashes are starting to grow in, as well as fingernails. The fingers and toes become fully separated, as well. As the fetus grows, the skin also goes through a lot of changes. It’s thought that by week 18 or so, the fetus is able to hear sounds like your heartbeat, and after that week, your voice and certain other outside noises. Around week 20, vernix starts to be produced. Vernix is the slippery white coating that covers the fetal skin and protects it from amniotic fluid. As more and more fat develops, the skin becomes less transparent, and the fetus starts to look more like a baby as it “fills out.” All the parts of the eyes are developed, and near week 20, the eyelids may open. Before this, the eyelids were shut. The fetus can’t really see, though, until later on in the third trimester.

Weeks 22 through 26:
By the time the fetus is 24 weeks, if you birthed the baby at this point, it would survive with medical technology. He/she is working on developing sleep/wake cycles, and even has a startle reflex by now! The nervous system is not fully developed yet, and the brain is picking up speed with development, as well. Air sacs in the lungs are beginning to form, but there’s still a long way to go yet.

Other things that occur during this trimester include the full development of the placenta, the thickening of the umbilical cord, hair growth on the head of the fetus, and the eyes move to the front of the face and the ears move from the neck to the sides of the head.

Next up: third trimester!

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