Risk Factors That Develop During Pregnancy
During pregnancy, a problem may occur or a condition may develop to make the pregnancy high risk. For example, pregnant women may be exposed to something that can produce birth defects (teratogens), such as radiation, certain chemicals, drugs, or infections. Or a disorder may develop. Some disorders are related to (are complications of) pregnancy.
Drugs
Some drugs taken during pregnancy cause birth defects (see Section 22, Chapter 259). Examples are alcohol, isotretinoin (used to treat severe acne), some anticonvulsants, lithium, some antibiotics (such as streptomycin, kanamycin, and tetracycline), thalidomide, warfarin, and angiotensin-converting enzyme (ACE) inhibitors (taken during the last two trimesters). Taking drugs that block the actions of folic acid (such as the immunosuppressant methotrexate or the antibiotic trimethoprim) can also cause birth defects (a deficiency of folic acid increases the risk of having a baby with a birth defect). Using cocaine may cause birth defects, premature detachment of the placenta (placental abruption), and premature birth. Smoking cigarettes increases the risk of having a baby with a low birth weight. Early in pregnancy, women are asked if they are using any of these drugs. Of particular concern are alcohol, cocaine, and cigarette smoking.
Disorders That Develop During Pregnancy
During pregnancy, women may develop disorders that are not directly related to pregnancy. Some disorders increase the risk of problems for pregnant women or the fetus. They include disorders that cause a high fever, infections, and disorders that require abdominal surgery. Certain disorders are more likely to occur during pregnancy because of the many changes pregnancy causes in a woman's body. Examples are thromboembolic disease, anemia, and urinary tract infections.
Fevers: A disorder that causes a temperature greater than 103° F (39.5° C) during the 1st trimester increases the risk of a miscarriage and defects of the brain or spinal cord in the baby. Fever late in pregnancy increases the risk of preterm labor.
Infections: Some infections that occur coincidentally during a pregnancy can cause birth defects. German measles (rubella) can cause birth defects, particularly of the heart and inner ear. Cytomegalovirus infection can cross the placenta and damage the fetus's liver and brain. Other viral infections that may harm the fetus or cause birth defects include herpes simplex and chickenpox (varicella). Toxoplasmosis, a protozoal infection, may cause miscarriage, death of the fetus, and serious birth defects. Listeriosis, a bacterial infection, can also harm the fetus. Bacterial infections of the vagina (such as bacterial vaginosis) during pregnancy may lead to preterm labor or premature rupture of the membranes containing the fetus. Treatment of infections with antibiotics may reduce the likelihood of these problems.
Disorders That Require Surgery: During pregnancy, a disorder that requires emergency surgery involving the abdomen may develop. This type of surgery increases the risk of preterm labor and can cause a miscarriage, especially early in pregnancy. Thus, surgery is usually delayed as long as possible unless the woman's long-term health may be affected.
If appendicitis develops during pregnancy, surgery to remove the appendix (appendectomy) is performed immediately because a ruptured appendix may be fatal. An appendectomy is not likely to harm the fetus or cause a miscarriage. However, appendicitis may be difficult to recognize during pregnancy. The cramping pain of appendicitis resembles uterine contractions, which are common during pregnancy. The appendix is pushed higher in the abdomen as the pregnancy progresses, so the location of pain due to appendicitis may not be what is expected.
If an ovarian cyst persists during pregnancy, surgery is usually postponed until after the 12th week of pregnancy. The cyst may be producing hormones that are supporting the pregnancy and often disappears without treatment. However, if a cyst or another mass is enlarging, surgery may be necessary before the 12th week. Such a mass may be cancerous.
Obstruction of the intestine during pregnancy can be very serious. If obstruction leads to gangrene of the intestine and peritonitis (inflammation of the membrane that lines the abdominal cavity), a woman may miscarry and her life is endangered. Exploratory surgery is usually performed promptly when pregnant women have symptoms of intestinal obstruction, particularly if they have had abdominal surgery or an abdominal infection.
Thromboembolic Disease: In the United States, thromboembolic disease is the leading cause of death in pregnant women. In thromboembolic disease, blood clots form in blood vessels. They may travel through the bloodstream and block an artery. The risk of developing thromboembolic disease is increased for about 6 to 8 weeks after delivery. Most complications due to blood clots result from injuries that occur during delivery. The risk is much greater after a cesarean section than after vaginal delivery.
Blood clots usually form in the superficial veins of the legs as thrombophlebitis or in the deep veins as deep vein thrombosis. Symptoms include swelling, pain in the calves, and tenderness. The severity of the symptoms does not correlate with the severity of the disease. A clot can move from the legs to the lungs, where it may block one or more arteries in the lungs. This blockage, called pulmonary embolism, can be life threatening. If a clot blocks an artery supplying the brain, a stroke can result. Blood clots can also develop in the pelvis.
Women who have had a blood clot during a previous pregnancy may be given heparin (an anticoagulant) during subsequent pregnancies to prevent blood clots from forming. If women have symptoms suggesting a blood clot, Doppler ultrasonography may be performed to check for clots. If a blood clot is detected, heparin is started without delay. Heparin may be injected into a vein (intravenously) or under the skin (subcutaneously). Heparin does not cross the placenta and cannot harm the fetus. Treatment is continued for 6 to 8 weeks after delivery, when the risk of blood clots is high. After delivery, warfarin may be used instead of heparin. Warfarin can be taken by mouth, has a lower risk of complications than heparin, and can be taken by women who are breastfeeding.
If pulmonary embolism is suspected, a lung ventilation and perfusion scan (see Section 4, Chapter 46) may be performed to confirm the diagnosis. This procedure involves injecting a tiny amount of a radioactive substance into a vein. The procedure is safe during pregnancy because the dose of the radioactive substance is so small. If the diagnosis of pulmonary embolism is still uncertain, pulmonary angiography is required.
Anemia: Most pregnant women develop some degree of anemia because they have an iron deficiency. The need for iron doubles during pregnancy, because iron is needed to make red blood cells in the fetus. Anemia may also develop during pregnancy because of a folic acid deficiency. Anemia can usually be prevented or treated by taking iron and folic acid supplements during pregnancy. However, if anemia becomes severe and persists, the blood's capacity to carry oxygen is decreased. As a result, the fetus may not receive enough oxygen, which is needed for normal growth and development, especially of the brain. Pregnant women who have severe anemia may become excessively tired, short of breath, and light-headed. The risk of preterm labor is increased. A normal amount of bleeding during labor and delivery can cause the anemia in these women to become dangerously severe. Women with anemia are more likely to develop infections after delivery. Also, if folic acid is deficient, the risk of having a baby with a birth defect of the brain or spinal cord, such as spina bifida, is increased.
Urinary Tract Infections: Urinary tract infections are common during pregnancy, probably because the enlarging uterus slows the flow of urine by pressing against the tubes that connect the kidneys to the bladder (ureters). When urine flow is slow, bacteria may not be flushed out of the urinary tract, increasing the risk of an infection. These infections increase the risk of preterm labor and premature rupture of the membranes containing the fetus. Sometimes an infection in the bladder or ureters spreads up the urinary tract and reaches a kidney, causing an infection there (see Section 22, Chapter 262). Treatment consists of antibiotic therapy.
Pregnancy Complications
Pregnancy complications are problems that occur only during pregnancy. They may affect the woman, the fetus, or both and may occur at different times during the pregnancy. For example, complications such as a mislocated placenta (placenta previa) or premature detachment of the placenta from the uterus (placental abruption) can cause bleeding from the vagina during the last 3 months of pregnancy. Women who bleed at this time are at risk of losing the baby or of bleeding excessively (hemorrhaging) or dying during labor and delivery. However, most pregnancy complications can be effectively treated.
 See the figure Ectopic Pregnancy: A Mislocated Pregnancy.
Some problems that result from hormonal changes during pregnancy cause only minor, transient symptoms in pregnant women. For example, the normal hormonal effects of pregnancy can slow the movement of bile through the bile ducts. Cholestasis of pregnancy may result. The most obvious symptom is itching all over the body (usually in the last few months of pregnancy). No rash develops. If itching is intense, cholestyramine may be given. The disorder usually resolves after delivery but tends to recur in subsequent pregnancies.
Hyperemesis Gravidarum: Hyperemesis gravidarum is extremely severe nausea and excessive vomiting during pregnancy. Hyperemesis gravidarum differs from ordinary morning sickness. If women vomit often and have nausea to such an extent that they lose weight and become dehydrated, they have hyperemesis gravidarum. If women vomit occasionally but gain weight and are not dehydrated, they do not have hyperemesis gravidarum. The cause of hyperemesis gravidarum is unknown.
Because hyperemesis gravidarum can be life threatening to pregnant women and the fetus, women who have it are hospitalized. An intravenous line is inserted into a vein to give fluids, sugar (glucose), electrolytes, and occasionally vitamins. Women who have this complication are not allowed to eat or drink anything for at least 24 hours. Sedatives, antiemetics, and other drugs are given as needed. After women are rehydrated and vomiting has subsided, they can begin eating frequent, small portions of bland foods. The size of the portions is increased if they can tolerate more food. Usually, vomiting stops within a few days. If symptoms recur, the treatment is repeated. Rarely, if weight loss continues and symptoms persist despite treatment, women are fed via a tube passed through the nose and down the throat to the small intestine for as long as necessary.
Preeclampsia: About 5% of pregnant women develop preeclampsia (toxemia of pregnancy). In this complication, an increase in blood pressure is accompanied by protein in the urine (proteinuria). Preeclampsia usually develops between the 20th week of pregnancy and the end of the first week after delivery. The cause of preeclampsia is unknown. But it is more common among women who are pregnant for the first time, who are carrying two or more fetuses, who have had preeclampsia in a previous pregnancy, who already have high blood pressure or a blood vessel disorder, or who have sickle cell disease. It is also more common among girls aged 15 and younger and among women aged 35 and older.
A variation of severe preeclampsia, called the HELLP syndrome, occurs in some women. It consists of the following:
- hemolysis (the breakdown of red blood cells)
- elevated levels of liver enzymes, indicating liver damage
- low platelet count, making blood less able to clot and increasing the risk of bleeding during and after labor.
In 1 of 200 women who have preeclampsia, blood pressure becomes high enough to cause seizures; this condition is called eclampsia. One fourth of the cases of eclampsia occur after delivery, usually in the first 2 to 4 days. If not treated promptly, eclampsia may be fatal.
Preeclampsia may lead to premature detachment of the placenta from the uterus (placental abruption). Babies of women who have preeclampsia are 4 or 5 times more likely to have problems soon after birth than babies of women who do not have this complication. Babies may be small because the placenta malfunctions or because they are born prematurely.
If mild preeclampsia develops early in the pregnancy, bed rest at home may be sufficient, but such women should see their doctor frequently. If preeclampsia worsens, women are usually hospitalized. There, they are kept in bed and monitored closely until the fetus is mature enough to be delivered safely. Antihypertensives may be needed (see Section 22, Chapter 259). A few hours before delivery, magnesium sulfate may be given intravenously to reduce the risk of seizures. If preeclampsia develops near the due date, labor is usually induced and the baby is delivered.
If preeclampsia is severe, the baby may be delivered by cesarean section, which is the quickest way, unless the cervix is already opened (dilated) enough for a prompt vaginal delivery. A prompt delivery reduces the risk of complications for women and the fetus. If blood pressure is high, drugs to lower blood pressure, such as hydralazine or labetalol, may be given intravenously before delivery is attempted. Treatment of the HELLP syndrome is usually the same as that of severe preeclampsia.
After delivery, women who have had preeclampsia or eclampsia are closely monitored for 2 to 4 days because they are at increased risk of seizures. As their condition gradually improves, they are encouraged to walk. They may remain in the hospital for a few days, depending on the severity of the preeclampsia and its complications. After returning home, these women may need to take drugs to lower blood pressure. Typically, they have a checkup at least every 2 weeks for the first few months after delivery. Their blood pressure may remain high for 6 to 8 weeks. If it remains high longer, the cause may be unrelated to preeclampsia.
Gestational Diabetes: About 1 to 3% of pregnant women develop diabetes during pregnancy. This disorder is called gestational diabetes. Unrecognized and untreated, gestational diabetes can increase the risk of health problems for pregnant women and the fetus and the risk of death for the fetus. Gestational diabetes is more common among obese women and among certain ethnic groups, particularly Native Americans, Pacific Islanders, and women of Mexican, Indian, and Asian descent.
Most women with gestational diabetes develop it because they cannot produce enough insulin as the need for insulin increases late in the pregnancy. More insulin is needed to control the increasing level of sugar (glucose) in the blood. Some women may have had diabetes before becoming pregnant, but it was not recognized until they became pregnant.
Some doctors routinely screen all pregnant women for gestational diabetes. Other doctors screen only women who have risk factors for diabetes, such as obesity and certain ethnic backgrounds. A blood test is used to measure the blood sugar level. Women who have gestational diabetes are usually taught to measure their blood sugar levels with a home blood sugar monitoring device.
Treatment consists of eliminating high-sugar foods from the diet, eating to avoid excess weight gain during the pregnancy, and, if the blood sugar level is high, taking insulin. After delivery, gestational diabetes usually disappears. However, many women who have gestational diabetes develop type 2 diabetes as they become older.
Rh Incompatibility: Rh incompatibility occurs when a pregnant woman has Rh-negative blood and the fetus has Rh-positive blood, inherited from a father who has Rh-positive blood. In about 13% of marriages in the United States, the man has Rh-positive blood and the woman has Rh-negative blood.
The Rh factor is a molecule that occurs on the surface of red blood cells of some people. Blood is Rh-positive if red blood cells have the Rh factor and Rh-negative if they do not. Problems can occur if the fetus's Rh-positive blood enters the woman's bloodstream. The woman's immune system may recognize the fetus's red blood cells as foreign and produce antibodies, called Rh antibodies, to destroy the fetus's red blood cells. The production of these antibodies is called Rh sensitization.
During a first pregnancy, Rh sensitization is unlikely, because no significant amount of the fetus's blood is likely to enter the woman's bloodstream until delivery. So the fetus or newborn rarely has problems. However, once a woman is sensitized, problems are more likely with each subsequent pregnancy in which the fetus's blood is Rh-positive. In each pregnancy, the woman produces Rh antibodies earlier and in larger amounts.
If Rh antibodies cross the placenta to the fetus, they may destroy some of the fetus's red blood cells. If red blood cells are destroyed faster than the fetus can produce new ones, the fetus can develop anemia. Such destruction is called hemolytic disease of the fetus (erythroblastosis fetalis) or of the newborn (erythroblastosis neonatorum (see Section 23, Chapter 264)). In severe cases, the fetus may die.
At the first visit to a doctor during a pregnancy, women are screened to determine whether they have Rh-positive or Rh-negative blood. If they have Rh-negative blood, their blood is checked for Rh antibodies and the father's blood type is determined. If he has Rh-positive blood, Rh sensitization is a risk. In such cases, the blood of pregnant women is checked for Rh antibodies periodically during the pregnancy. The pregnancy can proceed as usual as long as no antibodies are detected.
If antibodies are detected, steps may be taken to protect the fetus, depending on how high the antibody level is. If the level becomes too high, amniocentesis may be performed. In this procedure, a needle is inserted through the skin to withdraw fluid from the amniotic sac. The level of bilirubin (a yellow pigment resulting from the normal breakdown of red blood cells) is measured in the fluid sample. If this level is too high, the fetus is given a blood transfusion. Usually, additional transfusions are given until the fetus is mature enough to be safely delivered. Then labor is induced. The baby may need additional transfusions after birth. Sometimes no transfusions are needed until after birth.
As a precaution, women who have Rh-negative blood are given an injection of Rh antibodies at 28 weeks of pregnancy and within 72 hours after delivery of a baby who has Rh-positive blood, even after a miscarriage or an abortion. The antibodies given are called Rh0(D) immune globulin. This treatment destroys any red blood cells from the baby that may have entered the bloodstream of the women. Thus, there are no red blood cells from the baby to trigger the production of antibodies by these women, and subsequent pregnancies are usually not endangered.
Fatty Liver of Pregnancy: This rare disorder occurs toward the end of pregnancy. The cause is unknown. Symptoms include nausea, vomiting, abdominal discomfort, and jaundice. The disorder may rapidly worsen, and liver failure may develop. Diagnosis is based on results of liver function tests and may be confirmed by a liver biopsy. The doctor may advise immediate termination of the pregnancy. The risk of death for pregnant women and the fetus is high, but those who survive recover completely. Usually, the disorder does not recur in subsequent pregnancies.
Peripartum Cardiomyopathy: The heart's walls may be damaged late in pregnancy or after delivery, causing peripartum cardiomyopathy. The cause is unknown. Peripartum cardiomyopathy tends to occur in women who have had several pregnancies, who are older, who are carrying twins, or who have preeclampsia. In some women, heart function does not return to normal after pregnancy. They may develop peripartum cardiomyopathy in subsequent pregnancies. These women should not become pregnant again. Peripartum cardiomyopathy can result in heart failure (see Section 3, Chapter 25), which is treated.
Problems With Amniotic Fluid: Too much amniotic fluid (polyhydramnios) in the membranes containing the fetus (amniotic sac) stretches the uterus and puts pressure on the diaphragm of pregnant women. This complication can lead to severe breathing problems for the women or to preterm labor.
Too much fluid tends to accumulate when pregnant women have diabetes, are carrying more than one fetus (multiple pregnancy), or produce Rh antibodies to the fetus's blood. Another cause is birth defects in the fetus, especially a blocked esophagus or defects of the brain and spinal cord (such as spina bifida). About half the time, the cause is unknown.
Too little amniotic fluid (oligohydramnios) can also cause problems. If the amount of fluid is greatly reduced, the fetus's lungs may be immature and the fetus may be compressed, resulting in deformities; this combination of conditions is called Potter's syndrome.
Too little amniotic fluid tends to develop when the fetus has birth defects in the urinary tract, has not grown as much as expected, or dies. Other causes include the use of angiotensin-converting enzyme (ACE) inhibitors, such as enalapril or captopril, in the 2nd and 3rd trimesters. These drugs are given during pregnancy only when they must be used to treat severe heart failure or high blood pressure. Taking nonsteroidal anti-inflammatory drugs (NSAIDs) late in pregnancy can also reduce the amount of amniotic fluid.
Placenta Previa: Placenta previa is implantation of the placenta over or near the cervix, in the lower rather than the upper part of the uterus. The placenta may completely or partially cover the opening of the cervix. Placenta previa occurs in 1 of 200 deliveries, usually in women who have had more than one pregnancy or who have structural abnormalities of the uterus, such as fibroids.
Placenta previa can cause painless bleeding from the vagina that suddenly begins late in pregnancy. The blood may be bright red. Bleeding may become profuse, endangering the life of the woman and the fetus.
Ultrasonography helps doctors identify placenta previa and distinguish it from a placenta that has detached prematurely (placental abruption).
When bleeding is profuse, women may be hospitalized until delivery, especially if the placenta is located over the cervix. Women who bleed profusely may need repeated blood transfusions. When bleeding is slight and delivery is not imminent, doctors typically advise bed rest in the hospital. If the bleeding stops, women are usually encouraged to walk. If bleeding does not recur, they are usually sent home, provided that they can return to the hospital easily. A cesarean section is almost always performed before labor begins. If women with placenta previa go into labor, the placenta tends to become detached very early, depriving the baby of its oxygen supply. The lack of oxygen may result in brain damage or other problems in the baby.
Placental Abruption (Abruptio Placentae): Placental abruption is the premature detachment of a normally positioned placenta from the wall of the uterus. The placenta may detach incompletely (sometimes just 10 to 20%) or completely. The cause is unknown. Detachment of the placenta occurs in 0.4 to 3.5% of all deliveries. This complication is more common among women who have high blood pressure (including preeclampsia) and among women who use cocaine.
The uterus bleeds from the site where the placenta was attached. The blood may pass through the cervix and out the vagina as an external hemorrhage, or it may be trapped behind the placenta as a concealed hemorrhage. Symptoms depend on the degree of detachment and the amount of blood lost (which may be massive). Symptoms may include sudden continuous or crampy abdominal pain, tenderness when the abdomen is pressed, and shock. Premature detachment of the placenta can lead to widespread clotting inside the blood vessels (disseminated intravascular coagulation), kidney failure, and bleeding into the walls of the uterus, especially in pregnant women who also have preeclampsia. When the placenta detaches, the supply of oxygen and nutrients to the fetus may be reduced.
Doctors suspect premature detachment of the placenta on the basis of symptoms. Ultrasonography can confirm the diagnosis.
 See the figure Problems With the Placenta.
Women with premature detachment of the placenta are hospitalized. The usual treatment is bed rest. If symptoms lessen, women are encouraged to walk and may be discharged from the hospital. If bleeding continues or worsens (suggesting that the fetus is not getting enough oxygen) or if the pregnancy is near term, an early delivery is often best for the woman and the baby. If vaginal delivery is not possible, a cesarean section is performed.
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