The stages of fetal development areas follows: Conception- Conception orfertilization of an ovum by sperm takes place in the fallopian tube. Duringconception, sperm penetrates into the oocyte to complete the genetic make-up ofzygote. Many mitotic divisions occur, and the zygote passes through thefallopian tube into the uterus. Implantation- After one week offertilization, zygote attaches to the uterine wall, and the process is calledimplantation. Differentiation of cell in the zygote occurs, and forms an innercell mass, and trophoblast.
The inner cell mass develops into the embryo, andtrophoblast (outer cell mass) develops into embryonic membranes, amnion, andplacenta. To maintain the pregnancy, placenta produces many hormones. It alsocarries nutrients, and oxygen from mother to fetus, and waste materials fromfetus to mother. Embryonic stage- Cells dividerapidly, organs and external body structures are formed. From week 3 to week 8,nearly all organs of the embryo are formed except the brain, spinal cord, andlungs.
These 3 organs continue to form and develop until the end of pregnancy.Most of the birth defects take place during this stage. Development of the fetus andplacenta: Eight weeks after fertilization, the developing embryo is called a fetus.The organs and other body structures, which were already formed, continue to develop.The fetus fills the entire uterus, by 12 weeks. By 14 weeks, the gender of thefetus can be identified. The movement of the fetus can be felt between 16 to 20weeks. After about 24 weeks, the fetus is capable of surviving outside theuterus, if intensive care is provided.
The body fat reserves develop andamniotic fluid begins to reduce by the end of 7 months. The fetus can see and hear by theeighth month. By month 9, the lungs are developed fully, reflexes are developed,and the baby responds to sound, touch and light. The space is less and so, the movementof the fetus is restricted.
The fetus changes its position, and prepares itselffor labor, and delivery. The fetus is nearly 20 inches long, and weighs nearly7 pounds. The fetus is fully developed for delivery. Basic effects of pregnancy onmother are described below: Hormonal changes- During pregnancy,placenta increases the production of hormones like estrogen, and progesterone,which are required to maintain the pregnancy, and uterus development. Reproductive system changes- Therise in estrogen levels during pregnancy results in the increase in size of theuterus. Cervix and vagina becomes more vascular. Towards the end of pregnancy, thevagina becomes elastic, thus helping in the easy passage of the baby down thebirth canal during childbirth. The mucus in the cervix becomes thick, and thus,protects the uterus from microbes.
The breast enlarges as glands develops toprepare for milk production. Weight gain and nutrition- Weightgain during pregnancy is due to increased size of uterus, placenta, amnioticfluid, the fetus, and enlarged breasts. To ensure healthy development of the fetus,the nutrient requirement increases during pregnancy as the metabolic rate ofthe mother increases. Digestive system changes- The uncontrollablevomiting causes dehydration, and change in electrolyte balance. Progesteronerelaxes the smooth muscles of the stomach, and intestine, thereby, decreasingthe motility of the digestive tract. Bloating, constipation and abdominaldiscomfort are generally observed. Fibrous diet is prescribed to relieveabdominal pain and constipation.
Cardiovascular changes – The work onthe heart increases during pregnancy because more blood has to be ejected ateach beat. The heart has to pump blood through placenta, fetus, enlarged uterus,and abdomen. The blood supply to kidneys also increases so as to remove wasteof the fetus as well.
Other effects of pregnancy on themother are exhaustion, congested, and bloody nose, skin discoloration, discomfortwhile sleeping, shortness of breath, and mood swings.