The second trimester of pregnancy, which consists of weeks 13 through 27, is a time for continued growth and development of the fetus. In the first trimester, the pregnancy begins with a few cells. Those cells evolve into an embryo and then a fetus within weeks. The first trimester involves the formation of major organs and the systems within the body. Within the second trimester, the fetus becomes more refined and has a recognizably human form.

During the second trimester, there is great progress in fetal development. "Rapid brain growth occurs, sucking motions are made with the mouth and amniotic fluid is swallowed," says Christine Dunn, a registered nurse in Albuquerque, N.M. Baby's skin is almost transparent, and the eyebrows and head hair appear, she says.

Read on to see what else is going on with fetal development this trimester!

At 13 weeks, the fetus is still far too small to function outside of the womb, even with medical assistance. The fetus must undergo many more changes in order to survive. Fetal growth during the second trimester involves further development of all internal organs, external physical characteristics, nerves, glands and senses.

Content on this site is not a substitute for professional medical or healthcare advice, diagnosis or treatment, and may not be used for such purposes. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical question or condition. Reliance on information presented on this site is at your own risk. This site contains the opinions and views of other users. Given the interactive nature of this site, we cannot endorse, guarantee, or be responsible for the accuracy, efficacy, or veracity of any content generated by our users.