Baby Development in the Womb

In the Womb

• A baby spends most of its time in the womb in a sac of amniotic fluid. The placenta is an organ that develops during the pregnancy and filters the baby's incoming nourishment. The development of the brain and other organs is vital to the baby's ability to survive outside the womb. The development of the heart and lungs is particularly important. They are often the last organs to fully develop and are often the cause of problems in premature babies.

The First Trimester

• The first trimester of pregnancy starts when the mother has her last menstruation, and it ends at the end of the 13th week after that period. It's during this time that the baby develops from a fertilized egg into an embryo about 3 inches long. The baby develops the heart, liver and several other internal organs during this time. She will also have a spinal cord, ears, eyes, nostrils and a mouth. A woman can hear the baby's heartbeat through ultrasound during this trimester.

The Second Trimester

• The second trimester is a time of further development of the organs and tissues and lasts from the 14th week through week 27. The hair begins to develop during this time, as does the skin. The baby begins to move often, from punches and kicks to rolling over and making faces. At the end of the trimester, the baby has eyebrows, eyelashes and ribs. The baby grows from 3 inches to about 12 inches during this time.

The Third Trimster

• The third trimester gets the baby fully ready for life outside of his mother's womb. By this time, most of the baby's systems are in place, but they need this time to further develop and grow. The baby puts on his layer of fat during this time, particularly in the last few weeks of the pregnancy. Most babies gain at least four pounds during this trimester and end up weighing an average of 7 1/2 lbs.

Pregnancy Nutrition

• The baby's development largely depends on genetics and the type of nutrition that the mother takes in. Some birth defects can be avoided by taking a supplement of folic acid before the baby's conception and during the first trimester. Getting enough vitamins and iron are also important parts of prenatal care that can reduce the risk of some defects. Taking supplements of calcium, iron and a multivitamin have been shown to aid in babies' development in the womb.