Fetal Development

See the Journey from Conception to Birth…

Day One

Development begins now. When a sperm meets and penetrates an egg, it is called fertilization or conception. At that very moment, the genetic makeup of a new human being is complete. The fertilized egg then begins to travel through the Fallopian tube into the uterus, where it will attach the the wall of the uterus.If you are pregnant, you may notice your first missed menstrual period the second week after you had sex. Depending on the type of pregnancy test, you may not get an accurate result this early. Home pregnancy tests may show a “Not Pregnant” result when you may actually be pregnant.

Two Weeks

The baby is now called an embryo. A home pregnancy test should show positive at this point. The embryo is about 1/100 of an inch long. Implantation into your uterus already began in week one and will continue this week.

Four Weeks

The embryo is about 1/6 of an inch long and already has a head and trunk. Structures that will become the arms and legs, called limb buds, will begin to appear this week. His or her heartbeat can be heart via ultrasound at around 18-22 days. During this week, the eyes, ears, spine, kidneys, liver start to form.

Six Weeks

The embryo is about 1/2 an inch long and has a four-chambered heart that beats 150 times per minute. Activity can be detected in the developing brain and nervous system. The embryo has nostrils and a spine, and the fingers and eyelids are beginning to form. An ultrasound at this point could show him or her making slow body movements and even hiccups.

Eight Weeks

The embryo is about 1 1/5 inches long – about the size of a small plum. The beginnings of his or her key body parts are present, although they are not completely developed or positioned in their final locations. All organs are present, as well as the ears, fingers, toes, and teeth buds.

Ten Weeks

The fetus is about 2 1/2 inches from head to rump. The fingernails are beginning to develop and the body hair and external genitalia are present. Between 8 and 10 weeks, the fetus begins to make small, random movements and he or she can squint and open their mouth.

Twelve Weeks

The fetus is about 3 1/2 inches from head to rump and their boy and organs are complete. He or she is able to swallow and their kidneys are able to make urine. Blood begins to form in the bone marrow and a doctor may be able to tell you if it’s a boy or a girl by this time.

Fourteen Weeks

The fetus is about 4 3/4 inches from head to rump and his or her head is erect and their legs are developed. During an ultrasound, you could see their slow eye movements and see him or her suck their thumb.

Sixteen Weeks

The fetus is about 5 1/2 inches from head to rump and is now larger than the palm of your hand. He or she is now able to kick, swallow, and sleep.

Twenty Weeks

The fetus is about 7 1/2 inches from head to rump and he or she now has their own fingerprints. You will now be able to feel him or her move inside of your belly.



BettyFetal Development