Seeing the growth and development of a baby within a woman is an incredible experience. From the union of an egg and a sperm to the first, second, third, etc. division of the cells we can see a beautiful symphony of God's creation of a human. How in the world do the cells know if they should develop into bones or muscles or cute little toes?

Fertilization

Fertilization:  the joining of the egg and the sperm to form a unique human being.  The zygote has 46 chromosomes - 23 from the mother and 23 from the father. These chromosomes will help determine the baby's sex, traits such as eye and hair color, and, to some extent, personality and intelligence.

Soon after fertilization, the zygote travels down the fallopian tube toward the uterus. At the same time, it will begin dividing rapidly to form a cluster of cells resembling a tiny raspberry. The inner group of cells will become the embryo. The outer group of cells will become the membranes that nourish and protect it.

Week 4

When the zygote — now known as a blastocyst — reaches the uterus, it will burrow into the uterine wall for nourishment. The placenta, which will nourish the baby throughout the pregnancy, also begins to form.  Hormones produced by the embryo have stopped the mother's menstrual cycle.

* Technically, the age of this embryo is only 2 weeks since conception.  Obstetricians count "weeks of pregnancy" from the first day of a woman's last menstrual cycle (not from the date of actual fertilization) because there is often no way to determine exactly when conception occurred.  For the purposes of these pages, we will count weeks of pregnancy as obstetricians do; from the first day of the last menstrual cycle.  For the perspective of the age of the embryo since conception, subtract 2 weeks from the ages noted here.

Week 5

The fifth week of pregnancy, or the third week after conception, marks the beginning of the embryonic period. This is when the baby's brain, spinal cord, heart and other organs begin to form.

Week 6

Growth is rapid this week. Just four weeks after conception, the neural tube along the baby's back is closing and the baby's heart is pumping blood.

Basic facial features will begin to appear, including passageways that will make up the inner ear and arches that will contribute to the jaw. The baby's body begins to take on a c-shaped curvature. Small buds will soon become arms and legs.

By the end of this week, the baby may be 1/6 to 1/4 inch (4 to 6 millimeters) long.

Week 7

Seven weeks into the pregnancy, (or five weeks after conception,) the baby's brain and face are rapidly developing. Tiny nostrils become visible, and the eye lenses begin to form. The arm buds that sprouted last week now take on the shape of paddles. 

The baby has developed its own blood type, unique from the mother's. 

Week 8

Eight weeks into the pregnancy, or six weeks after conception, the baby's arms and legs are growing longer, and fingers have begun to form.

The baby may begin to move this week, but the mother won't be able to feel it yet. The upper lip and nose have formed. The trunk of the baby's body is beginning to straighten.

At the end of week 8, the embryonic period ends and the fetal stage begins.

Continue to 2nd Trimester