Fetal Development Stages
From the moment of conception a fetus is rapidly growing and developing. In the first month of gestation the fetus is an embryo consisting of two layers of cells from which all of his organs and body parts will mature. By the ninth month the typical baby weighs almost 7 pounds and is more than 19 inches long. There are a multitude of milestones that take place during the approximately 40 weeks of the average pregnancy.
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Pre-Conception to Week 2
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Technically, you are not pregnant in the first week or two of the 40 weeks of your pregnancy. Conception generally takes place about two weeks after the start of your period, but your due date is figured by counting ahead 40 weeks from the start date of your last period, even though you were not yet pregnant.
When a sperm enters the mother's egg cell, the ensuing cell is called a zygote. The zygote contains all of the required genetic information (DNA) to become a child. The zygote continues to divide as it moves down the Fallopian tube, creating an inner group of cells (the future embryo) with an outer shell (to nourish and shelter it).This stage is called a blastocyst.
Weeks 2 to 4
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By this time the lining of the uterus has grown and is ready to sustain a baby. When the blastocyst reaches the womb (uterus) it bonds securely to the lining, where it is nourished through the mother's bloodstream.
By now the cells of the embryo are multiplying and assuming specific functions, a process known as differentiation, when various blood cells, kidney cells and nerve cells are created. At this point the fetus is taking form.
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First Trimester
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During weeks five through 13, a number of changes occur in the womb. The heart, spinal cord and brain begin to develop; arm and leg buds become visible and soon grow longer.
As the first trimester wraps up, the genitals of the fetus are identifiable. The developing heart is now beating at a regular rhythm, all vital organs are forming and tooth buds emerge for the baby teeth.
Second Trimester
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By the second trimester you may have heard your baby's heartbeat during your monthly prenatal doctor visits. As you adjust to your growing abdomen in weeks 13 to 27, you baby now has operational organs, nerves and muscles. You may begin to feel your baby moving in your abdomen.
During the second trimester fine hair (lanugo) develops on the head and eyebrows and eyelashes come into view. The mouth makes sucking gestures. By the end of this trimester the fetal heartbeat can be heard with a stethoscope.
Third Trimester
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Your baby is entering the final stages of development in the third trimester. During weeks 24 to 40, air sacs are developing in the lungs. There is also accelerated brain development and the nervous system is sophisticated enough to control some body functions
As the third and final trimester continues, the baby's body fat is on the increase and fingernails continue beyond the end of the fingertips. Tiny breast buds have developed on both males and females.
Prenatal Care
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You can plan on weekly checkups during the last month of pregnancy. As your delivery date approaches, your health care provider will continue to check your blood pressure and weight, as well as your baby's heart rate and movements.
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