Pregnancy is the condition a female experiences from the moment of conception (fertilization of the egg by sperm) until the birth of the baby. The period of gestation is generally 38 weeks, or nine months. This gestation period is marked by numerous fetal developments and culminates in childbirth. The mother's egg carries 23 chromosomes; the father's sperm carries 23 chromosomes as well. When they unite, the 46 chromosomes hold the information that makes the baby unique, such as hair color. Two specific chromosomes determine the baby's gender, one from each parent. Two "X" chromosomes make a girl; an "X" and a "Y" make a boy. Women can only contribute an "X" chromosome, so it is the sperm that determines the baby's sex.
Medical professionals break down the nine months of pregnancy into three "trimesters," or three-month periods. Pregnant females should undergo prenatal care during every trimester to safeguard the health and development of the baby.
Excellent prenatal care and education can eliminate or reduce risks for mother and baby. Low birth weight (under five and a half pounds), which is associated with a 300 percent increase in other birth defects, is one complication that can be prevented by quality medical care.
Regular prenatal visits can detect problems such as anemia (low iron and oxygen levels in the blood), gestational diabetes, and pre-eclampsia (marked by swelling, high blood pressure, and protein in the urine). These conditions are treatable when detected early, but if left untreated they may threaten the lives of both mother and baby.
Prenatal visits should commence as soon as a woman discovers she is pregnant. The first prenatal exam will confirm pregnancy and evaluate the woman's general health.
Through the seventh month of pregnancy, the pregnant woman should attend regular monthly checkups. During these exams, the doctor will evaluate the growth of the fetus; he will listen to the heartbeat and measure the woman's uterus to make sure the baby is growing normally. The mother's weight, blood pressure, blood, and urine will be tested. He may also check the hands and feet for signs of edema (swelling) and perform a Pap smear to check for changes in the cervix.
In the eighth month, the expectant mother should visit the doctor every two weeks; in the ninth month, she should see the doctor every week. The doctor performs the standard prenatal exams as well as new tests to check on the size and position of the baby. The physician will also check on the woman's cervix; if the cervix is soft, it indicates that the baby will be born soon.
Some women undergo screening tests during pregnancy. Her doctor will evaluate each woman and decide on an individual basis if she needs a particular test. These tests alert doctors of potential problems with the fetus:
Alpha-Fetoprotein (AFP) or Maternal Serum Screening
This test analyzes the mother's blood. The AFP test looks for abnormalities in the fetus's brain or spinal cord; it can also check for chromosomal disorders such as Down syndrome. This test poses no danger to the mother or baby, so most women will undergo AFP screening between 15 and 18 weeks. A possible drawback to the AFP test is the number of false-positive results it produces; abnormal results will require further testing.
Ultrasound
This screening test uses sound waves to construct a picture of the fetus without the danger of X-ray. Ultrasound can determine a woman's due date if performed early enough in the pregnancy. It can tell a doctor if a woman is carrying multiple fetuses, determine the condition of the placenta, and check for a breech position prior to delivery. It can also identify the cause of problems such as vaginal bleeding and others. This test can be performed from the fifth week of pregnancy until delivery. Generally, it is performed after the 16th week.
Chorionic Villus Sampling (CVS)
In CVS testing, the doctor takes a sample of the chorionic villi from the placenta via a needle passed through the abdomen or via a tube passed through the vagina and cervix. This test can detect fetal defects as early as the ninth week of pregnancy. This test is not recommended for all women. Women who already have a child with birth defects, who have a family history of birth defects, who are at least age 35 on their due date, and women at risk for certain genetic diseases (or women with an at-risk partner) are candidates for CVS.
Amniocentesis
During amniocentesis, the doctor sticks a needle into the woman's amniotic sac via the abdomen to extract some of the fluid surrounding the fetus. Analysis of this fluid can detect a number of problems, such as Down syndrome, Tay-Sachs disease, and neural tube defects, among others. This test is given to women with the same risk factors as the women who undergo CVS testing. A small risk of miscarriage (0.5 percent) is associated with amniocentesis.
During her pregnancy, the mother must insure that she is giving her baby enough nutrients through her food intake. If the mother lacks nutrients, the baby will as well. The average healthy woman gains between 25 and 35 pounds during pregnancy, although there is no magic number.
During the first 20 weeks, the woman will generally gain 10 pounds, followed by one pound per week for the remainder of the pregnancy. The average weight gained can be broken down in this fashion: seven pounds in maternal stores; four pounds in increased fluid volume; four pounds in increased blood volume; two pounds in breast enlargement; two pounds in the uterus; and six to eight pounds for the baby.
Usually a woman will gain more weight with multiple gestation-twins, triplets, or even more fetuses during one pregnancy. When the babies develop from one egg and one sperm, they are monozygotic, or identical, twins. When they develop from two eggs each fertilized by a separate sperm, they are known as dyzygotic, or fraternal, twins. Identical twins are always the same sex; fraternal twins may or may not be the same sex. Identical twins occur in about one of every 250 pregnancies. In North America, fraternal twins occur in approximately one of every 80 pregnancies.
One of every 14 babies born in the United States in 1990 was born with a birth defect, many of which were preventable. Alcohol consumption, including wine, beer, and hard liquor, can cause serious harm to a fetus. Research has not yet proven how much alcohol is too much for a growing fetus, so medical professionals caution pregnant women not to drink at all. Drugs, especially illegal ones, pose a serious risk to the baby and may result in birth defects or complications during childbirth. Cigarette smoking during pregnancy can result in premature delivery, low birth weight, and intellectual deficiencies for the baby later in childhood.
