Fetal Growth & Development What is Happening?

Pregnancy evokes many emotions which may include curiosity regarding the growth and development of your unborn child. These emotions are intensified during the nine months of nurturing. Many people think of pregnancy in terms of months. However, pregnancy is broken down into the gestational age of the fetus by weeks and trimesters. Gestational age of the fetus is calculated from the last menstrual period. Pregnancy is really ten lunar months, 40 weeks or 280 days, which is considered to be a full term pregnancy. Pregnancy is divided into three trimesters.

First Trimester
The first trimester includes the first day of your last menstrual period and extends until 12 weeks of gestation. At five weeks, your baby reaches a half inch in length and weighs less than an ounce and is called an embryo. Amazingly, the circulatory system and other vital organs have begun to form, including the heart, brain, lungs, eyes and ears. Tiny limb buds emerge which will ultimately grow into arms and legs. The placenta and umbilical cord are developing, and the baby is well protected from harm in a sac of liquid called amniotic fluid. At this time the heart beat will be seen by vaginal probe on ultrasound. By the end of eight weeks the embryo is about one inch long. The arms and legs are starting to form, and the embryo is beginning to look more human. Fingers and toes are growing and facial features are becoming more prominent. The head seems big compared to the body because the brain is growing at a very rapid rate. At this point, the embryonic period ends and all essential structures are present.


Second Trimester
The second trimester begins at the end of 12 weeks. The baby is now called a fetus. It is starting to grow faster and is now four inches long. Fingernails and toenails are growing and, for some, a little hair may appear. At this point, the baby�s heartbeat with a Doppler may be detectable. By 16 weeks, many women begin to – look� pregnant. After all, the fast-growing fetus is now six to seven inches long and weighs about five ounces. The baby�s teeth, eyelids, and eyelashes are developing in detail. If you could see inside the uterus, you could determine the sex of the baby. By 20 weeks you may feel that little flutter of life that is the baby moving. This is known as quickening. At twenty-four weeks, the fetus resembles a miniature infant except for its reddish, wrinkled skin. The baby is ten to twelved inches in length and weighs approximately eleven ounces.

Third Trimester
The third trimester begins after the first 28 weeks. During this trimester your baby gains most of his/her weight. The fetus is usually very active, alternating between sleep and wake cycles. With special care, babies born now can survive. An infant is considered full-term after the thirty-sixth week of gestation. At this time the baby�s lungs are ready to breathe on their own. The process from fertilization of the egg to a living human being is remarkable. The miracle is not just the birth of the child but that of a healthy newborn.

Editorial provided by Tierney Matthews RNC, MSN, and Mary De Ritter RN, BSN Englewood Hospital and Medical Center in New Jersey.