Human Fetal Development in the Second Trimester
The second trimester of pregnancy starts at week 13 and finishes at the end of week 27, according to the Mayo Clinic.
This stage may also be referred to as the fourth, fifth and sixth months of pregnancy.
Weight and Length
Towards the end of the second trimester, the fetus will be approximately 9 inches (230 mm) long, from crown to rump and weigh almost 2 lbs. (820 g). The length may have tripled since the first trimester.
During the subsequent trimester, the fetal sex gets obvious and potentially distinguished during a ultrasound. By week 23, the uterus and ovaries are in place for a girl and the testes are beginning to descend for a boy.
The fetal ears begin to stand out at the side of the head and the nerve endings from the brain connect to the ears allowing the fetus to hear, according to the Mayo Clinic. The head is about half of the overall size of the fetus.
The baby develops quickly during the fifth month and interior organs keep on developing. Fetal muscle and body fat is being stored under the skin and body hair starts to appear.
Vernix, a substance that protects the skin, and lanugo, a soft downy hair, cover the fetal body during the sixth month. Fingers have developed fingerprints that are unique to her.