This information is intended for general educational purposes only and should never be relied upon as a substitute for professional medical advice.

Years ago, while giving an anesthetic for a ruptured tubal pregnancy (at two months) I was handed what I believed to be the smallest human being ever seen. The embryo sac was intact and transparent. Within the sac was a tiny human male, swimming extremely vigorously in the amniotic fluid, while attached to the wall by the umbilical cord. The tiny human was perfectly developed, with long, tapering fingers, feet and toes. It was almost transparent as regards to the skin, and the delicate arteries and veins were prominent to the ends of the fingers. The baby was extremely alive and did not look at all like the photos and drawings of 'embryos' which I have seen. When the sac was opened, the tiny human immediately lost its life and took on what is accepted as the appearance of an embryo at this stage, blunt extremities, etc. - Paul E. Rockwell, M.D.

DID YOU KNOW… 

Pregnancy is counted from the first day of a woman's last period. This means that at conception, the unborn child is already considered two weeks old!

Week 2

Conception is the moment at which the sperm penetrates the ovum. Once fertilized it is called a zygote, until it reaches the uterus 3-4 days later.

Week 4

The embryo may float freely in the uterus for about 48 hours before implanting. Upon implantation, complex connections between the mother and embryo develop to form the placenta.

Week 6

The embryo is about 1/5 of an inch in length. A primitive heart is beating. Head, mouth, liver, and intestines begin to take shape

Week 10

The embryo is now about 1 inch in length. Facial features, limbs, hands feet fingers and toes become apparent. The nervous system is responsive and many of the internal organs begin to function.

Week 14

The fetus is now 3 inches long and weighs almost an ounce. The muscles begin to develop and sex organs form. Eyelids, fingernails, and toenails also form. The child's spontaneous movements can  be observed.

Week 18

The fetus is now about 5 inches long. The child blinks, grasps, and moves her mouth. Hair grows on the head and body.

Week 22

The fetus now weighs approximately 1/2 a pound and spans about 10 inches from head to toe. Sweat glands develop, and the external skin has turned from transparent to opaque.

Week 26

The fetus can now inhale, exhale and even cry. Eyes have completely formed, and the tongue has developed taste buds. Under intensive medical care the fetus has a over a 50% chance of surviving outside the womb.

Week 30

The fetus is usually capable of living outside the womb and would be considered premature at birth.

Week 40

This marks the end of the normal gestational period. The child is now ready to live outside of his mother's womb.

Obstetricians count "weeks of pregnancy" from the first day of a woman's last menstrual cycle because there is often no way to determine exactly when conception occurred. Embryologists, however, typically describe the developing embryo or fetus by the number of weeks since conception. To determine the age of the unborn child since conception using this table, subtract two weeks.