Prenatal Development

When you’re pregnant, you watch the ultrasounds carefully and marvel at every nuance of fetal development. It is a fascinating process, and today’s technology means we’re lucky to be able to watch the rapid changes a fetus undergoes.

When an embryo becomes a fetus at eight weeks’ gestation, development is rapid. What can parents-to- be expect when it comes to prenatal development?

Healthline.com offers a concise breakdown of prenatal development, which follows development from 9 to 38 weeks, or full term. While the first trimester begins at conception, what is referred to as fetal development begins at 9 weeks.

Even at just 9 to 12 weeks gestational age, the fetus is able to make a fist and his liver starts developing red blood cells. The head is still large; about half the size of the fetus, but external features such as the limbs, genitals, and face are already developed.

The second trimester, weeks 12 through 24, is marked by rapid growth and change. During weeks 13 to 15, the fetus is develops lanugo, a fine, first hair, and his lungs, muscles, and bones, as well as other structures, continue to develop. At this relatively early age of prenatal development, the fetus can swallow.

Between weeks 16 and 20, fat begins to develop under the skin, and smaller features like nails, brows, and eyelashes appear. Mothers-to-be will attest to the developing strength of the fetus since they can begin to feel fetal movements during this stage of prenatal development.

Weeks 21 through 24 are a period of rapid weight and length gain; the fetus is about 11 inches and over a pound and a half by the end of week 20. The startle reflex that newborns exhibit develops at this time, and the lungs continue to develop.

The third trimester is marked by rapid growth of the brain and nervous system. The fetus starts to gain greater control over his movements between weeks 25 and 28, and the lungs have developed enough to breathe air.

By the end of week 32, fat deposits are more pronounced and the lungs, while immature, begin breathing movements. Bones are present, but not yet hardened, at this stage of prenatal development.

During weeks 33 to 36, the fetus continues to gain body fat, the lanugo begins to disappear, and the fetus is about 5 and a half to 6 and a half pounds. A high degree of control over body functions has developed, and the fetus is around 16 to 19 inches long.

Week 38 marks full prenatal development; between weeks 36 and 38, thicker hair on the head replaces lanugo, and, in a healthy fetus, all the organs are functioning. Prenatal development is complete, and baby is ready to be born.

Prenatal development is truly miraculous; from two cells comes a fully-developed fetus and then a baby. Although, except in ultrasounds, and through feeling fetal movement, mothers-to-be are unable to monitor this development, the process is an amazing journey that happens in a brief, but intense, period of time.