When most people think of pregnancy, they probably picture a woman with a large, rounded tummy who is close to giving birth. But that picture changes for many expectant moms the minute their pregnancy is confirmed, because after their first trip to the obstetrician or midwife, they begin to realize that the time period before they begin to show is the most sensitive and crucial time for development for the baby.

Here, two women's health experts describe the process of development each baby goes through from conception to delivery.

After the egg is fertilized in a woman's fallopian tube, it then moves into the uterus. It takes a week from conception before the egg is even implanted, and about two weeks after conception it can be called an embryo, says Dr. Lillian Schapiro, an OB/GYN and women's health expert with Peachtree Women's Specialists in Atlanta, Ga.

"The first things to form are the nervous system, brain and circulatory system," Dr. Schapiro says. "Twenty-five days after conception the heart is actually beating, although it is smaller than a pea. The eyes, ears and mouth begin to form around this time period too, and by the 28th day, the arm and leg buds are in place."

According to Margaret Buxton, a certified nurse-midwife with the West End Women's Health Center in Nashville, Tenn., the baby's spine closes by five weeks, which is why doctors advise taking folic acid even before conception to prevent problems such as spinal bifida in infants.

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