The period from conception to birth. After the egg is fertilized by a sperm and then implanted in the lining of the uterus, it develops into the placenta and embryo, and later into a fetus. Pregnancy usually lasts 40 weeks, beginning from the first day of the woman's last menstrual period, and is divided into three trimesters, each lasting three months.
Pregnancy is a state in which a woman carries a fertilized egg inside her body. Due to technological advances, pregnancy is increasingly occurring among older women in the United States.
At the end of the first month, the embryo is about a third of an inch long, and its head and trunk-plus the beginnings of arms and legs-have started to develop. The embryo receives nutrients and eliminates waste through the umbilical cord and placenta. By the end of the first month, the liver and digestive system begin to develop, and the heart starts to beat.
In this month, the heart starts to pump and the nervous system (including the brain and spinal cord) begins to develop. The 1 in (2.5 cm) long fetus has a complete cartilage skeleton, which is replaced by bone cells by month's end. Arms, legs and all of the major organs begin to appear. Facial features begin to form.
By now, the fetus has grown to 4 in (10 cm) and weighs a little more than an ounce (28 g). Now the major blood vessels and the roof of the mouth are almost completed, as the face starts to take on a more recognizably human appearance. Fingers and toes appear. All the major organs are now beginning to form; the kidneys are now functional and the four chambers of the heart are complete.
The fetus begins to kick and swallow, although most women still can't feel the baby move at this point. Now 4 oz (112 g), the fetus can hear and urinate, and has established sleep-wake cycles. All organs are now fully formed, although they will continue to grow for the next five months. The fetus has skin, eyebrows, and hair.
Now weighing up to a 1 lb (454 g) and measuring 8-12 in (20-30 cm), the fetus experiences rapid growth as its internal organs continue to grow. At this point, the mother may feel her baby move, and she can hear the heartbeat with a stethoscope.
Even though its lungs are not fully developed, a fetus born during this month can survive with intensive care. Weighing 1-1.5 lbs (454-681 g), the fetus is red, wrinkly, and covered with fine hair all over its body. The fetus will grow very fast during this month as its organs continue to develop.
There is a better chance that a fetus born during this month will survive. The fetus continues to grow rapidly, and may weigh as much as 3 lb (1.3 kg) by now. Now the fetus can suck its thumb and look around its watery womb with open eyes.
Growth continues but slows down as the baby begins to take up most of the room inside the uterus. Now weighing 4-5 lbs (1.8-2.3 kg) and measuring 16-18 in (40-45 cm) long, the fetus may at this time prepare for delivery next month by moving into the head-down position.
Adding 0.5 lb (227 g) a week as the due date approaches, the fetus drops lower into the mother's abdomen and prepares for the onset of labor, which may begin any time between the 37th and 42nd week of gestation. Most healthy babies will weigh 6-9 lb (2.7-4 kg) at birth, and will be about 20 in. long.
The first sign of pregnancy is usually a missed menstrual period, although some women bleed in the beginning. A woman's breasts swell and may become tender as the mammary glands prepare for eventual breastfeeding. Nipples begin to enlarge and the veins over the surface of the breasts become more noticeable.
Nausea and vomiting are very common symptoms and are usually worse in the morning and during the first trimester of pregnancy. They are usually caused by hormonal changes, in particular, increased levels of progesterone. Women may feel worse when their stomach is empty, so it is a good idea to eat several small meals throughout the day, and to keep things like crackers on hand to eat even before getting out of bed in the morning.
Many women also feel extremely tired during the early weeks. Frequent urination is common, and there
Pregnancy usually lasts 40 weeks in humans, beginning from the first day of the woman's last menstrual period, and is divided into three trimesters. The illustration above depicts the position of the developing fetus during each trimester.
(Illustration by Electronic Illustrators Group.)may be a creamy white discharge from the vagina. Some women crave certain foods, and an extreme sensitivity to smell may worsen the nausea. Weight begins to increase.
In the second trimester (13-28 weeks) a woman begins to look noticeably pregnant and the enlarged uterus is easy to feel. The nipples get bigger and darker, skin may darken, and some women may feel flushed and warm. Appetite may increase. By the 22nd week, most women have felt the baby move. During the second trimester, nausea and vomiting often fade away, and the pregnant woman often feels much better and more energetic. Heart rate increases as does the volume of blood in the body.
By the third trimester (29-40 weeks), many women begin to experience a range of common symptoms. Stretch marks may develop on abdomen, breasts, and thighs, and a dark line may appear from the navel to pubic hair. A thin fluid may be expressed from the nipples. Many women feel hot, sweat easily and often find it hard to get comfortable. Kicks from an active baby may cause sharp pains, and lower backaches are common. More rest is needed as the woman copes with the added stress of extra weight. Braxton Hicks contractions may get stronger.
At about the 36th week in a first pregnancy (later in repeat pregnancies), the baby's head drops down low into the pelvis. This may relieve pressure on the upper abdomen and the lungs, allowing a woman to breathe more easily. However, the new position places more pressure on the bladder.
A healthy gain for most women is between 25 and 35 pounds. Women who are overweight should gain less; and women who are underweight should gain more. On average, pregnant women need an additional 300 calories a day. Generally, women will gain three to five pounds in the first three months, adding one to two pounds a week until the baby is born. An average, healthy full-term baby at birth weighs 7.5 lb (3.4 kg), and the placenta and fluid together weigh another 3.5 lb. The remaining weight that a woman gains during pregnancy is mostly due to water retention and fat stores. Her breasts, for instance, gain about 2 lb. in weight, and she gains another 4 lb due to the increased blood volume of pregnancy.
In addition to the typical, common symptoms of pregnancy, some women experience other problems that may be annoying, but which usually disappear after delivery. Constipation may develop as a result of food passing more slowly through the intestine. Hemorrhoids and heartburn are fairly common during late pregnancy. Gums may become more sensitive and bleed more easily; eyes may dry out, making contact lenses feel painful. Pica (a craving to eat substances other than food) may occur. Swollen ankles and varicose veins may be a problem in the second half of pregnancy, and chloasma may appear on the face.
Chloasma, also known as the "mask of pregnancy" or melasma, is caused by hormonal changes that result in blotches of pale brown skin appearing on the forehead, cheeks, and nose. These blotches may merge into one dark mask. It usually fades gradually after pregnancy, but it may become permanent or recur with subsequent pregnancies. Some women also find that the line running from the top to the bottom of their abdomen darkens. This is called the linea nigra.
While the above symptoms are all considered to be normal, there are some symptoms that could be a sign of a more dangerous underlying problem. A pregnant woman with any of the following signs should contact her doctor immediately:
Many women first discover they are pregnant after a positive home pregnancy test. Pregnancy urine tests check for the presence of human chorionic gonadotropin (hCG), which is produced by a placenta. The newest home tests can detect pregnancy on the day of the missed menstrual period.
Home pregnancy tests are more than 97% accurate if the result is positive, and about 80% accurate if the result is negative. If the result is negative and there is no menstrual period within another week, the pregnancy test should be repeated. While home pregnancy tests are very accurate, they are less accurate than a pregnancy test conducted at a lab. For this reason, women may want to consider having a second pregnancy test conducted at their doctor's office to be sure of the accuracy of the result.
Blood tests to determine pregnancy are usually used only when a very early diagnosis of pregnancy is needed. This more expensive test, which also looks for hCG, can produce a result within nine to 12 days after conception.
Once pregnancy has been confirmed, there are a range of screening tests that can be done to screen for birth defects, which affect about 3% of unborn children. Two tests are recommended for all pregnant women: alpha-fetoprotein (AFP) and the triple marker test.
Other tests are recommended for women at higher risk for having a child with a birth defect. This would include women over age 35, who had another child or a close relative with a birth defect, or who have been exposed to certain drugs or high levels of radiation. Women with any of these risk factors may want to consider amniocentesis, chorionic villus sampling (CVS) or ultrasound.
Prenatal care is vitally important for the health of the unborn baby. A pregnant woman should be sure to eat a balanced, nutritious diet of frequent, small meals. Women should begin taking 400 mcg of folic acid several months before becoming pregnant, as folic acid has been shown to reduce the risk of spinal cord defects, such as spina bifida.
No medication (not even a nonprescription drug) should be taken except under medical supervision, since it could pass from the mother through the placenta to the developing baby. Some drugs, called teratogens, have been proven harmful to a fetus, but no drug should be considered completely safe (especially during early pregnancy). Drugs taken during the first three months of a pregnancy may interfere with the normal formation of the baby's organs, leading to birth defects. Drugs taken later on in pregnancy may slow the baby's growth rate, or they may damage specific fetal tissue (such as the developing teeth), or cause preterm birth.
To have the best chance of having a healthy baby, a pregnant woman should avoid:Women should begin following a healthy diet even before they become pregnant. This means cutting back on high-calorie, high-fat, high-sugar snacks, and increasing the amount of fruits, vegetables and whole grains in her diet. Once she becomes pregnant, she should make sure to get at least six to 11 servings of breads and other whole grains, three to five servings of vegetables, two to four servings of fruits, four to six servings of milk and milk products, three to four servings of meat and protein foods, and six to eight glasses of water. She should limit caffeine to no more than one soft drink or cup of coffee per day.
Pregnancy is a natural condition that usually causes little discomfort provided the woman takes care of herself and gets adequate prenatal care. Childbirth education classes for the woman and her partner help prepare the couple for labor and delivery.
Alpha-fetoprotein — A substance produced by a fetus' liver that can be found in the amniotic fluid and in the mother's blood. Abnormally high levels of this substance suggests there may be defects in the fetal neural tube, a structure that will include the brain and spinal cord when completely developed. Abnormally low levels suggest the possibility of Down' syndrome.
Braxton Hicks' contractions — Short, fairly painless uterine contractions during pregnancy that may be mistaken for labor pains. They allow the uterus to grow and help circulate blood through the uterine blood vessels.
Chloasma — A skin discoloration common during pregnancy, also known as the "mask of pregnancy" or melasma, in which blotches of pale brown skin appear on the face. It is usually caused by hormonal changes. The blotches may appear in the forehead, cheeks, and nose, and may merge into one dark mask. It usually fades gradually after pregnancy, but it may become permanent or recur with subsequent pregnancies. Some women may also find that the line running from the top to the bottom of their abdomen darkens. This is called the linea nigra.
Embryo — An unborn child during the first eight weeks of development following conception (fertilization with sperm). For the rest of pregnancy, the embryo is known as a fetus.
Fetus — An unborn child from the end of the eights week after fertilization until birth. Human chorionic gonadotropin (hCG) — A hormone produced by the placenta during pregnancy.Placenta — The organ that develops in the uterus during pregnancy that links the blood supplies of the mother and baby.
Rhythm method — The oldest method of contraception with a very high failure rate, in which partners periodically refrain from having sex during ovulation. Ovulation is predicted on the basis of a woman's previous menstrual cycle.
Spina bifida — A congenital defect in which part of the vertebrae fail to develop completely, leaving a portion of the spinal cord exposed.
There are many ways to avoid pregnancy. A woman has a choice of many methods of contraception which will prevent pregnancy, including (in order of least to most effective):
Healthy Mothers, Healthy Babies National Coalition. 409 12th St., Washington, DC 20024. (202) 638-5577.
National Institute of Child Health and Human Development. 9000 Rockville Pike, Bldg. 31, Rm. 2A32, Bethesda, MD 20892. (301) 496-5133.
Positive Pregnancy and Parenting Fitness. 51 Saltrock Rd., Baltic, CT 06330. (203) 822-8573.the condition of having a developing embryo or fetus in the body, after union of an oocyte (ovum) and spermatozoon . The average gestation period for a human pregnancy is 10 lunar months (280 days) from the first day of the last menstrual period.
Conception . Once a month an ovum (secondary oocyte) matures in one of the ovaries and travels down the nearby fallopian tube to the uterus ; this process is called ovulation . At Fertilization , which must take place within a day or two of ovulation, one of the spermatozoa unites with the ovum to form a zygote . The zygote then implants itself in the wall of the uterus, which is richly supplied with blood, and begins to grow. (See also reproduction .)
Signs of Pregnancy . Usually the first indication of pregnancy is a missed menstrual period. Unless the period is more than 10 days late, however, this is not a definite indication, since many factors, including a strong fear of pregnancy, can delay menstruation. Nausea, or morning sickness , usually begins in the fifth or sixth week of pregnancy. About 4 weeks after conception, changes in the breasts become noticeable: there may be a tingling sensation in the breasts, the nipples enlarge, and the areolae (dark areas around nipples) may become darker. Frequent urination, another early sign, is the result of expansion of the uterus, which presses on the bladder.
Other signs of pregnancy include softening of the cervix and filling of the cervical canal with a plug of mucus. Early in labor this plug is expelled and there is slight bleeding; expulsion of the mucous plug is known as show and indicates the beginning of cervical dilatation. chadwick's sign of pregnancy refers to a bluish color of the vagina which is a result of increased blood supply to the area.
When the abdominal wall becomes stretched there may be a breaking down of elastic tissues, resulting in depressed areas in the skin which are smooth and reddened. These markings are called striae gravidarum . In subsequent pregnancies the old striae appear as whitish streaks and frequently do not disappear completely.
There are several fairly accurate laboratory tests for pregnancy; all are designed to detect human chorionic gonadotropin (hCG), a hormone produced by living chorionic placental tissue and evident in the blood and urine of pregnant women. See also pregnancy tests .
Growth of the Fetus . The average pregnancy lasts about 280 days, or 40 weeks, from the date of conception to childbirth. Since the exact date of conception usually is not known, the estimated date of delivery can be calculated using nägele's rule . This is approximate, since pregnancy may be shorter than the average or can last as long as 300 days. (For stages of growth of the fetus, see fetus .)
Care of the Fetus . A host of influences can adversely affect the growth and development of the fetus and his or her chances for survival and good health after birth. The diet of the mother should be nutritious and well-balanced so that the fetus receives the necessary food elements for development and maturity of body structures. It is especially important that the mother receive adequate protein in her diet, because a protein deficiency can hamper fetal intellectual development. Supplemental iron and vitamins usually are recommended during pregnancy.
There is now less emphasis on severe restriction of the mother's dietary intake to maintain a limited weight gain. The average gain is about 28 lb during pregnancy, and either starvation diets or forced feedings can be unhealthy for the mother and hazardous for the fetus. Ideally, the mother should achieve normal weight before she becomes pregnant because obesity increases the possibility of eclampsia and other serious complications of pregnancy. Mothers who are underweight are more likely to deliver immature babies who, by virtue of their physiologic immaturity, are more likely to suffer from birth defects, hyaline membrane disease , and other developmental disorders of the newborn.
Other factors affecting the fetus include certain drugs taken by the mother during pregnancy. A well-known example is thalidomide, which inhibits the growth of the extremities of the fetus, resulting in gross deformities. Many drugs, including prescription as well as nonprescription medications, are now believed to be capable of causing fetal abnormalities. In addition, consumption of alcohol during pregnancy may result in fetal alcohol syndrome . Most health care providers recommend that all drugs be avoided during pregnancy except those essential to the control of disease in the mother.
Diseases that increase the risk of obstetrical complications include diabetes, heart disease, hypertension, kidney disease, and anemia. rubella (German measles) can be responsible for many types of birth defects, particularly if the mother contracts it in the first 3 months of pregnancy. Sexually transmitted diseases can have tragic effects on the baby, even though the symptoms in the mother are minor at the time of pregnancy. syphilis is particularly dangerous because it is one of the few diseases that can be transmitted to the fetus in utero. The baby is either stillborn or born infected, and rarely escapes physical or mental defects or both. Successful treatment of the mother before the fifth month of pregnancy will prevent infection in the infant.
During the birth process the infant may be infected with gonorrhea as it passes through the birth canal. Gonorrheal infection of the eyes can cause blindness. herpes simplex Type II involving the genitals of the mother can also be transmitted to the infant at birth. The mortality and morbidity rates for such infected infants are high.
The age of the mother is also an important factor in the well-being of the fetus. The mortality and morbidity rate for infants born of mothers below age 15 and above 40 are higher than for those of mothers between these ages.
Recently developed tests to monitor fetal health have taken much of the guesswork out of predicting the chances of survival and health status of the fetus after birth. Such tests and evaluation techniques include amniocentesis , chemical and hormonal assays, biophysical profiles, testing for alpha-fetoprotein, ultrasound examinations, electronic surveillance of fetal vital signs and reaction to uterine contractions, and analyses of the infant's blood during labor.
Prenatal Care . The care of the mother during her entire pregnancy is important to her well-being and that of the fetus she is carrying. It will help provide ease and safety during pregnancy and childbirth. The health care provider learns about the patient's physical condition and medical history, and can detect possible complications before they become serious.
On the first prenatal visit the patient's medical history is taken in considerable detail, including any diseases or operations she has had, the course of previous pregnancies, if any, and whether there is a family history of multiple births or of diabetes mellitus or other chronic diseases. The first visit also includes a thorough physical examination and measurement of the pelvis. Blood samples are taken for screening for rubella and sexually transmitted diseases such as syphilis, hepatitis B, chlamydiosis, infection by the human immunodeficiency virus, and other conditions. A complete blood count is also needed. Urine is tested for albumin and sugar and examined microscopically. On subsequent visits the patient brings a urine specimen, collected upon arising that morning, to be tested for albumin and glucose. At each prenatal visit her blood pressure is taken and recorded and she is weighed. In the second trimester, when the uterus becomes an abdominal organ, the height of the fundus is measured at each visit. After the sixth month a rule such as mcdonald's rule can be applied to assess fetal growth.
Patients who are considered high-risk mothers usually are sent to a specialist and the infant is delivered at a regional hospital where sophisticated monitoring equipment and laboratory tests are available, and specially trained personnel can attend to the needs of the mother and her infant.
Discomforts and Complications. morning sickness usually appears in the early months of pregnancy and rarely lasts beyond the third month. Often it requires no treatment or can be relieved by such simple measures as eating dry crackers and tea before rising. Indigestion and heartburn are best prevented by avoiding foods that are difficult to digest, such as cucumbers, cabbage, cauliflower, spinach, onions, and rich foods. Constipation usually can be corrected by diet or a mild laxative; strong laxatives should not be used unless prescribed by the health care provider.
A visit to a dentist early in pregnancy is a good idea to forestall any possibility of infection arising from tooth decay. Pregnancy does not encourage tooth decay. Hemorrhoids sometimes occur in pregnancy because of pressure from the enlarged uterus on the veins in the rectum. The health care provider should be consulted for treatment. varicose veins also result from pressure of the uterus, which restricts the flow of blood from the legs and feet. Lying flat with the feet raised on a pillow several times a day will help relieve swelling and pain in the legs. In more difficult cases the health care provider may prescribe an elastic bandage or support stockings.
Backache during pregnancy is caused by the heavy abdomen pulling on muscles that are not normally used, and can be relieved by rest, sensible shoes, and good posture. Swelling of the feet and ankles usually is relieved by rest and by remaining off the feet for a day or two. If the swelling does not disappear, the health care provider should be informed since it may be an indication of a more serious complication.
Shortness of breath is common in the later stages of pregnancy. If at any time it becomes so extreme that the woman cannot climb a short flight of stairs without discomfort, the health care provider should be consulted. If a mild shortness of breath interferes with sleep, lying in a half-sitting position, supported by several pillows, may help.
The more serious complications of pregnancy include pyelitis , hyperemesis gravidarum , eclampsia , and placenta previa and abruptio placentae .
