The Stages of Baby Development in the Mother

An average pregnancy lasts about 40 weeks. During that time, the fetus goes through an amazing journey inside its mother's womb. From humble beginnings as a single cell, to a creature that looks more tadpole than human, to a recognizable baby that sucks its thumb and turns somersaults, the stages of how a baby develops inside its mother have intrigued expectant parents since the dawn of time.

Zygote

• A zygote is a single-celled organism that results from the fusion of a man's sperm and a woman's egg. It contains one set of DNA from each parent. During the first week, the zygote divides quickly until it is composed of multiple cells.

Blastocyst

• Once the zygote divides into multiple cells, it becomes known as the blastocyst. The blastocyst implants itself in the mother's womb approximately 10 to 14 days after fertilization. At this time, the mother may experience a little light bleeding that many women mistake for a menstrual period. The blastocyst eventually divides into two parts. One part will become the placenta, and the other part continues to develop into an embryo.

Embryo

• There is some disagreement in the medical community about when a blastocyst becomes an embryo. Most doctors put the time frame at anywhere from 5 to 12 weeks. The embryo is about the size of a grain of rice. It has a tail instead of legs and looks vaguely like an alien life form. Its heart, liver, kidneys and lungs begin to form.

Fetus--Second Trimester

• As the mother finishes her third month of pregnancy, the embryo gets another new name--the fetus. By the fourth month of pregnancy, the fetus has developed a heartbeat that can be measured with specialized equipment. At the end of the fourth month, doctors can determine the gender of the fetus through ultrasound. By this time, the fetus has become aware of its mother's heartbeat and sounds going on outside the womb. During the fifth month, "quickening" occurs, and the mother feels the fetus move inside her for the first time. By the sixth month, all essential organs except the lungs are formed, and the facial features are recognizable as human.

Fetus--Third Trimester

• During the seventh month, the fetus is considered legally viable. In actuality, however, a fetus born at 28 weeks has only a 10 percent to 20 percent chance of survival, because its lungs are not yet developed enough to sustain life outside the mother's body. The eighth month is a time of growth and of rapid brain development. By the ninth month, the fetus' lungs have matured, and it is ready to be born. In preparation, it drops lower into its mother's pelvis and positions itself so that its head is pointing toward the vagina. Its life as a baby is about to begin.