The first three months of pregnancy are marked by morning sickness, a heartbeat, and fingers and toes. Learn the details of you and your child's development during the exiting first trimester.

How Mom Develops

Morning sickness and decreased energy dominates the first trimester for about 50% of pregnant women, as rapidly increasing estrogen levels and quick uterine growth throw your body on a chemical rollercoaster.

Early pregnancy symptoms for many women also include dizziness, light-headedness, irritability, fatigue, headaches, and indigestion. Not all women experience these symptoms, and many women fly through the first trimester with no side effects whatsoever. The only symptomatic concern occurs when symptoms like sickness suddenly halt. A physician should be contacted if this occurs.

How Baby Develops

For more information and color photographs of fetal development, check out the Fetal Development Overview, which includes specific information about each stage of the unborn child's development.

Fertilization occurs at the two-week mark, where the 46 chromosomes of the sperm and the egg join in the fallopian tube to determine all physical characteristics. The fertilized egg is no larger than the head of a pin. The zygote then makes its way toward the uterus.

Blastocyst is the name for the rapidly developing embryo searching for a place to implant itself into the wall of the uterus during week three and four. Once buried under the lining of the uterus, the backbone, spinal coumn, kidneys, liver, intestines, and nervous system begin to develop.

The heart begins beating at five weeks, and the brain begins to develop. Growing to reach the size of a raisin, facial features begin to be visible, including the eyes, mouth and tongue in the 7th week. Blood cell growth has encouraged the muscle system to develop, and the unborn child begins to move around. By this stage blood cells have given the baby its own blood type.

Brain waves can be measured at 8 weeks, when the amnionic sac has filled with fluid to allow the fetus to move around freely. Arms and legs are growing rapidly, and toes are on their way. The baby measures about 1/2 " at this stage.

The placenta is now providing the oxygen for the baby to breathe instead of blood, which has now been diverted through it's almost fully-formed heart. At this, the 10-week mark, the baby develops its teeth.

Crying becomes possible at 12 weeks, when vocal chords have formed fully (although the cry is silent due to the amnionic fluid). The child can feel pain at this point, due to the fully developed brain and nervous system, and may also suck her thumb. New eyelids cover the eyes to protect optical nerves until the 7th month, when they will open once more.