Risk Factors

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. 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 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.

Infection:

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.

Appendicitis:

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.

Ovarian cyst

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 intestine:

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.

Pulmonary embolism:

If pulmonary embolism is suspected, a lung ventilation and perfusion scan 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. Treatment consists of antibiotic therapy.