Second Trimester: Fetal Development

The second trimester is from week 13 through 28. For many women the second trimester is the easiest. Morning sickness and fatigue subside leaving your more energetic and feeling like your old self again.

Second Trimester Fetal Development Milestones

Weeks 14 thru 16 – Gestational Age (Fetal age – Weeks 12 thru 14):

The fetus’s skin is transparent and a fine hair called lanugo begins to form on the head. The fetus begins sucking and swallows bits of amniotic fluid. Fingerprints which individualize each human being have now developed on the tiny fingers of the fetus. Meconium is made in the intestinal tract and will build up to be the baby’s first bowel movement. Flutters may be felt in the mom’s growing abdomen, as the fetus begins to move around more. Sweat glands have developed, and the liver and pancreas produce fluid secretions. The fetus has reached 6 inches in length and weighs about 4 ounces.

Weeks 17 thru 20 – Gestational Age (Fetal Age – Weeks 15 thru 18):

The baby has reached a point where movements are being felt more often by the mother. The eyebrows and eyelashes grow in, and tiny nails have begun to grow on the fingers and toes. The skin of the fetus is going through many changes and begins to produce vernix in the twentieth week. Vernix is a white pasty substance that covers the fetus’ skin to protect it from amniotic fluid. A fetal heartbeat can be heard by a stethoscope now. The fetus has reached a length of 8 inches and weighs about 12 ounces.

Weeks 21 thru 23 – Gestational Age (Fetal Age – Weeks 19 thru 21):

Lanugo now covers the fetus’s entire body. The fetus is beginning to have the look of a newborn infant as the skin becomes less transparent while fat begins to develop. All the components of the eyes are developed. The liver and pancreas are working hard to develop completely. The fetus has reached about 10-11 inches in length and weighs about 1 – 1 ¼ pound.

Weeks 24 thru 26 – Gestational Age (Fetal Age – Weeks 22 thru 24)-
Beginning the third trimester:

If your baby was delivered now, it could survive with the assistance of medical technology. The fetus has developed sleeping and waking cycles and mom will begin to notice when each of these takes place. The fetus has a startle reflex, and the air sacs in the lungs have begun formation. The brain will be developing rapidly over the next few weeks. The nervous system has developed enough to control some functions. The fetus has reached about 14 inches in length and weighs about 2 ¼ pounds.

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