A baby undergoes rapid fetal development in the nine months he spends in his mother’s womb. A pregnancy is usually measured in 40 weeks of gestation, but many people prefer to measure it in months. The three main stages of development are ovulation/conception, embryonic development and development of the fetus.
Ovulation usually occurs around week two of the cycle. In the two weeks prior to conception, the body is readying the womb for a potential pregnancy by growing a layer of rich, blood perfused tissue. After conception, which takes place about two weeks into the cycle, the egg makes its way to the uterus, where it is implanted and begins its rapid growth.
Embryonic Development is the most critical stage of fetal development, when the systems are undergoing important foundational development. The embryonic state of development takes place from conception to approximately the 11th week of pregnancy. After the second week, the development of the embryo is in full swing. At four weeks, cellular division continues, with the cells dividing between the those that will make up the placenta and those that will make up the baby.
By six weeks, the baby’s heartbeat has begun and her arms and legs are developing. At eight weeks, the intestines begin to form and teeth start growing under the gums. By the end of the embryonic stage of fetal development, the embryo has developed joints and the beginning of the irises. Major organs have begun their development, as well as the central nervous system.
Fetal Development begins after the 11th week, when the baby is called a fetus. From the 11th to 16th week, the fetus begins developing distinguishable genitals, hair, nails and vocal chords. The kidneys begin to process bodily fluids, and the liver begins to function as it should. Bones also begin to harden at this time.
From the 16th to 20th week, the baby undergoes another rapid growth spurt. He begins to develop fat under a thin skin. The heart pumps a staggering 25 quarts of blood every day. Meconium, a baby’s waste product, accumulates in the bowel. The fetus regularly hiccups and spends the same amount of time awake and asleep as a typical newborn.
Fetal development slows down during the 21st to 24th weeks. The eyelids and eyebrows are usually completely formed by this time, and if the fetus is a boy, his testes begin to descend from the pelvis. By the 24th week, the baby will weigh approximately 1.3 pounds (.6 kilograms).
During the period of time from the 25th to the 28th week, the baby continues to develop. Lung development is marked during this time, as the baby prepares to breathe air at birth. By the 28th week, 90% of babies born will survive, although breathing may be an issue. The lungs begin to secrete surfactant, which is necessary for breathing. Ligaments form, nostrils open and brain development proceeds at a fast rate. The baby’s retinas begin to form, and she can completely open her eyes at this point.
From the 29th to the 40th week, fetal development is focused on the development of the lungs. For the most part, all of the major systems and organs are complete. The baby’s job is to fatten up to face the environment outside of the protective womb. The baby begins to develop immunities needed to survive. At 37 weeks, the baby will continue to add approximately one ounce (28.35 grams) per day to his body weight. This week marks a pregnancy as full term, and the baby should be delivered with no complications.