Some risk factors are present before women become pregnant. These risk factors include certain physical and social characteristics of women, problems that have occurred in previous pregnancies, and certain disorders women already have.
Physical Characteristics
The age, weight, and height of women affect risk during pregnancy. Girls aged 15 and younger are at increased risk of preeclampsia (a type of high blood pressure that develops during pregnancy). Young girls are also at increased risk of having underweight (small-for-gestational-age) or undernourished babies. Women aged 35 and older are at increased risk of problems such as high blood pressure, gestational diabetes (diabetes that develops during pregnancy), and complications during labor.
Women who weigh less than 100 pounds before becoming pregnant are more likely to have small, underweight babies. Obese women are more likely to have very large babies,which may be difficult to deliver. Also, obese women are more likely to develop gestational diabetes and preeclampsia.
Women shorter than 5 feet are more likely to have a small pelvis, which may make movement of the fetus through the pelvis and vagina (birth canal) difficult during labor. For example, the fetus's shoulder is more likely to lodge against the pubic bone. This complication is called shoulder dystocia (see Labor and Delivery Complications: Shoulder Dystocia). Also, short women are more likely to have preterm labor and a baby who has not grown as much as expected.
Structural abnormalities in the reproductive organs increase the risk of a miscarriage. Examples are a double uterus or a weak (incompetent) cervix that tends to open (dilate) as the fetus grows.
Social Characteristics
Being unmarried or in a lower socioeconomic group increases the risk of problems during pregnancy. The reason these characteristics increase risk is unclear but is probably related to other characteristics that are more common among these women. For example, these women are more likely to smoke and less likely to consume a healthy diet and to obtain appropriate medical care.
Problems in a Previous Pregnancy
When women have had a problem in one pregnancy, they are more likely to have a problem, often the same one, in subsequent pregnancies. Such problems include having had a premature baby, an underweight baby, a baby that weighed more than 10 pounds, a baby with birth defects, a previous miscarriage, a late (postterm) delivery (after 42 weeks of pregnancy), Rh incompatibility that required a blood transfusion to the fetus, or a delivery that required a cesarean section. If women have had a baby who died shortly after birth, they are also more likely to have problems in subsequent pregnancies.
Women may have a condition that tends to make the same problem recur. For example, women with diabetes are more likely to have babies that weigh more than 10 pounds at birth.
Women who had a baby with a genetic disorder or birth defect are more likely to have another baby with a similar problem. Genetic testing of the baby, even if stillborn, and of both parents may be appropriate before another pregnancy is attempted (see Genetic Disorders Detection: Genetic Screening). If these women become pregnant again, tests such as ultrasonography, chorionic villus sampling, and amniocentesis may help determine whether the fetus has a genetic disorder or birth defect.
Having had six or more pregnancies increases the risks of very rapid labor and excessive bleeding after delivery. It also increases the risk of a mislocated placenta (placenta previa (see Pregnancy at High Risk: Placenta Previa).
Disorders Present Before Pregnancy
Before becoming pregnant, women may have a disorder that can increase the risk of problems during pregnancy. These women should talk with a doctor and try to get in the best physical condition possible before they become pregnant. After they become pregnant, they may need special care, often from an interdisciplinary team. The team may include an obstetrician (who may also be a specialist in the disorder), a specialist in the disorder, and other health care practitioners (such as nutritionists).
Heart Disease: Most women who have heart disease—including heart valve disorders (such as mitral valve prolapse) and some birth defects of the heart—can safely give birth to healthy children, without any permanent ill effects on heart function or life span. However, women who have heart failure before pregnancy are at considerable risk of problems.
Pregnancy requires the heart to work harder. Consequently, pregnancy may worsen heart disease or cause heart disease to produce symptoms for the first time. Usually, serious problems, including death of the woman or fetus, occur only when heart disease is severe before the woman becomes pregnant. About 1% of women who have severe heart disease before becoming pregnant die as a result of the pregnancy, usually because of heart failure.
The risk of problems increases throughout pregnancy as demands on the heart increase. Pregnant women with heart disease may become unusually tired and may need to limit their activities. Rarely, women with severe heart disease are advised to have an abortion early in pregnancy. Risk is also increased during labor and delivery. After delivery, women with severe heart disease may not be out of danger for at least 6 months, depending on the type of heart disease.
Heart disease in pregnant women may affect the fetus. The fetus may be born prematurely. Women with birth defects of the heart are more likely to have children with similar birth defects. Ultrasonography can detect some of these defects before the fetus is born. If severe heart disease in a pregnant woman suddenly worsens, the fetus may die.
During labor, women who have severe heart disease may be given an epidural anesthetic, which blocks sensation in the lower spinal cord and prevents women from pushing. Pushing during labor strains the heart, because it increases the amount of blood returning to the heart. Because pushing is not possible, the baby may have to be delivered with forceps.
For women with some types of heart disease, pregnancy is inadvisable because it so increases their risk of death. Primary pulmonary hypertension and Eisenmenger's syndrome are examples. If women who have one of these disorders become pregnant, doctors advise them to terminate the pregnancy as early as possible.
High Blood Pressure: Women who have high blood pressure (chronic hypertension) before they become pregnant are more likely to have potentially serious problems during pregnancy. These problems include preeclampsia (a type of high blood pressure that develops during pregnancy (see Pregnancy at High Risk: Preeclampsia), worsening of high blood pressure, a fetus that does not grow as much as expected, premature detachment of the placenta from the uterus (placental abruption), and stillbirth.
For most women with moderately high blood pressure (140/90 to 150/100 millimeters of mercury [mm Hg]), treatment with antihypertensive drugs is not recommended. Such treatment does not seem to reduce the risk of preeclampsia, premature detachment of the placenta, or a stillbirth nor to improve the growth of the fetus. However, some women are treated to prevent pregnancy from causing episodes of even higher blood pressure (which require hospitalization).
For women whose blood pressure is higher than 150/100 mm Hg, treatment with anti-hypertensive drugs is recommended (see Antihypertensive Drugs). Treatment can reduce the risk of stroke and other complications due to very high blood pressure. Treatment is also recommended for women who have high blood pressure and a kidney disorder because if high blood pressure is not controlled well, the kidneys may be damaged further.
Most antihypertensive drugs used to treat high blood pressure can be used safely during pregnancy. However, angiotensin-converting enzyme (ACE) inhibitors are discontinued during pregnancy, particularly during the last two trimesters. These drugs can cause severe kidney damage in the fetus. As a result, the baby may die shortly after birth.
During pregnancy, women with high blood pressure are monitored closely to make sure blood pressure is well controlled, the kidneys are functioning normally, and the fetus is growing normally. However, premature detachment of the placenta cannot be prevented or anticipated. Often, a baby must be delivered early to prevent stillbirth or complications due to high blood pressure (such as stroke) in the woman.
Anemia: Having a hereditary anemia, such as sickle cell disease, hemoglobin S-C disease, and some thalassemias, increases the risk of problems during pregnancy. Before delivery, blood tests are routinely performed to check for hemoglobin abnormalities in women who are at increased risk of having these abnormalities because of race, ethnic background, or family history. Chorionic villus sampling or amniocentesis may be performed to detect a hemoglobin abnormality in the fetus.
Women who have sickle cell disease are particularly at risk of developing infections during pregnancy. Pneumonia, urinary tract infections, and infections of the uterus are the most common. About one third of pregnant women who have sickle cell disease develop high blood pressure during pregnancy. A sudden, severe attack of pain, called sickle cell crisis, may occur during pregnancy as at any other time. Heart failure and blockage of arteries of the lungs by blood clots (pulmonary embolism), which may be life threatening, may also occur. Bleeding during labor or after delivery may be more severe. The fetus may grow slowly or not as much as expected. The fetus may even die. The more severe sickle cell disease was before pregnancy, the higher the risk of health problems for pregnant women and the fetus and the higher the risk of death for the fetus during pregnancy. With regular blood transfusions, women are less likely to have sickle cell crises but are more likely to reject the transfused blood. This condition, called alloimmunization, can be life threatening. Also, transfusions to pregnant women do not reduce risks for the fetus.
Kidney Disorders: Women with a severe kidney disorder before pregnancy are more likely to have problems during pregnancy. Kidney function may rapidly worsen during pregnancy. High blood pressure, which often accompanies a kidney disorder, may also worsen, and preeclampsia (a type of high blood pressure that develops during pregnancy) may develop. The fetus may not grow as much as expected or may be stillborn. In pregnant women who have a kidney disorder, kidney function and blood pressure are monitored closely as is the growth of the fetus. Often, the baby must be delivered early.
Women who have had a kidney transplant that has been in place for 2 or more years are usually able to safely give birth to healthy babies if their kidneys are functioning normally, if they have had no episodes of rejection, and if their blood pressure is normal. Many women who have a kidney disorder and who undergo hemodialysis regularly can also give birth to healthy babies.
Seizure Disorders: For most women who take anticonvulsants to treat a seizure disorder, the frequency of seizures does not change during pregnancy. However, sometimes the dose of the anticonvulsant must be increased.
Taking anticonvulsants increases the risk of birth defects (see ). Women who take anticonvulsants should discuss the risk of birth defects with an expert in the field, preferably before they become pregnant. Some women may be able to safely discontinue anticonvulsants during pregnancy, but most women should continue to take the drugs. The risks resulting from not taking the drugs (resulting in more frequent seizures, which can harm the fetus and the woman) usually outweigh the risks resulting from taking them during pregnancy.
Sexually Transmitted Diseases: Women who have a sexually transmitted disease may have problems during pregnancy. Chlamydial infection may cause preterm labor and premature rupture of the membranes containing the fetus. It can also cause conjunctivitis in newborns, as can gonorrhea. Syphilis in pregnant women may be transmitted to the fetus through the placenta. Syphilis can cause several birth defects.
About one fourth of pregnant women who have untreated human immunodeficiency virus (HIV) infection, which causes AIDS, transmit it to their baby (see Viral Infections: Human Immunodeficiency Virus (HIV) Infection). Experts recommend that women with HIV infection take antiretroviral drugs during pregnancy. When pregnant women take these drugs, the risk of transmitting HIV to their baby is reduced to less than 2%. For some women with HIV infection, delivery by cesarean section, planned in advance, may further reduce the risk of transmitting HIV to the baby. Pregnancy does not seem to accelerate the progress of HIV infection in women.
Genital herpes can be transmitted to a baby during a vaginal delivery. A baby who is infected with herpes can develop a life-threatening brain infection called herpes encephalitis. If herpes produces sores in the genital area late in pregnancy, women are usually advised to give birth by cesarean section, so that the virus is not transmitted to the baby. If no sores are present, the risk of transmission is very low.
Diabetes: For women who have diabetes before they become pregnant, the risks of complications during pregnancy depend on how long diabetes has been present and whether complications of diabetes, such as high blood pressure and kidney damage, are present. (In some women, diabetes develops during pregnancy; this disorder is called gestational diabetes (see Pregnancy at High Risk: Gestational Diabetes).
The risk of complications during pregnancy can be reduced by controlling the level of sugar (glucose) in the blood. The level should be kept as nearly normal as possible throughout pregnancy. Measures to control the blood sugar level (such as diet, exercise, and insulin
)
should be started before pregnancy (see Diabetes Mellitus (DM): Treatment). Most pregnant women are asked to measure their blood sugar level several times a day at home. Controlling diabetes is particularly important late in pregnancy. Then, the blood sugar level tends to increase because the body becomes less responsive to insulin
. A higher dose of insulin
is usually needed.
If diabetes is poorly controlled very early in the pregnancy, the risks of early miscarriage and significant birth defects are increased. When diabetes is poorly controlled later in pregnancy, the fetus is large and the risk of stillbirth is increased. A large fetus is less likely to pass easily through the vagina and is more likely to be injured during vaginal delivery. Consequently, delivery by cesarean section is often necessary. The risk of preeclampsia (a type of high blood pressure that occurs during pregnancy) is also increased for women with diabetes.
The fetus's lungs tend to mature slowly. If an early delivery is being considered (for example, because the fetus is large), the doctor may remove and analyze a sample of the fluid that surrounds the fetus (amniotic fluid). This procedure, called amniocentesis, helps the doctor determine whether the fetus's lungs are mature enough for the newborn to breathe air.
Newborns of women with diabetes are at increased risk of having low sugar, low calcium, and high bilirubin levels in the blood. Hospital staff members measure the levels of these substances and observe the newborns for symptoms of these abnormalities.
For women with diabetes, the requirement for insulin
drops dramatically immediately after
delivery. But the requirement usually returns to what it was before pregnancy within about 1 week.
Liver and Gallbladder Disorders: Women who have chronic viral hepatitis or cirrhosis (scarring of the liver) are more likely to miscarry or to give birth prematurely. Cirrhosis can cause varicose veins to develop around the esophagus (esophageal varices). Pregnancy slightly increases the risk of massive bleeding from these veins, especially during the last 3 months of pregnancy.
Pregnant women who develop gallstones are closely monitored. If a gallstone blocks the gallbladder or causes an infection, surgery may be necessary. This surgery is usually safe for pregnant women and the fetus.
Asthma: In about half of the women who have asthma and become pregnant, the frequency or severity of asthma attacks does not change during pregnancy. About one fourth of the women improve during pregnancy, and about one fourth get worse. If pregnant women with severe asthma are treated with prednisone
, the risk that the fetus will not grow as much as
expected or will be born prematurely is increased.
Because asthma can change during pregnancy, doctors may ask women with asthma to use a peak flow meter to monitor their breathing more often. Pregnant women with asthma should see their doctor regularly so that treatment can be adjusted as needed. Maintaining good control of asthma is important. Inadequate treatment can result in serious problems. Cromolyn
, bronchodilators (such as albuterol
), and corticosteroids (such as
beclomethasone
) can be taken during pregnancy. Inhalation is the preferred way for taking
these drugs. When inhaled, the drugs affect mainly the lungs and affect the whole body and the fetus less. Aminophylline
(taken by mouth or given intravenously) and theophylline
(taken by mouth) are occasionally used during pregnancy. Corticosteroids are taken by mouth only when other treatments are ineffective. Being vaccinated against the influenza virus during the influenza (flu) season is particularly important for pregnant women with asthma.
Autoimmune Disorders: The abnormal antibodies produced in autoimmune disorders can cross the placenta and cause problems in the fetus. Pregnancy affects different autoimmune disorders in different ways.
Systemic lupus erythematosus (lupus) may appear for the first time, worsen, or become less severe during pregnancy. How a pregnancy affects the course of lupus cannot be predicted, but the most common time for flare-ups is immediately after delivery.
Women who develop lupus often have a history of repeated miscarriages, fetuses that do not grow as much as expected, and preterm delivery. If women have complications due to lupus (such as kidney damage or high blood pressure), the risk of death for the fetus or newborn is increased.
In pregnant women, lupus antibodies may cross the placenta to the fetus. As a result, the fetus may have a very slow heart rate, anemia, a low platelet count, or a low white blood cell count. However, these antibodies gradually disappear over several weeks after the baby is born, and the problems they cause resolve except for the slow heart rate.
In Graves' disease, antibodies stimulate the thyroid gland to produce excess thyroid hormone. These antibodies can cross the placenta and stimulate the thyroid gland in the fetus. As a result, the fetus may have a rapid heart rate and may not grow as much as expected. The fetus's thyroid gland may enlarge, forming a goiter. Very rarely, a goiter may be so large that it interferes with delivery through the vagina.
Usually, women with Graves' disease take the lowest possible effective dose of propylthiouracil, which slows the activity of the thyroid gland. Physical examinations and measurements of thyroid hormone levels are performed regularly because propylthiouracil crosses the placenta and may prevent the fetus from producing enough thyroid hormone. Often, Graves' disease becomes less severe during the 3rd trimester, so the dose of propylthiouracil can be reduced or stopped. If necessary, the thyroid gland of pregnant women may be removed during the 2nd trimester. These women must begin taking thyroid hormone 24 hours after surgery. Taking this hormone causes no problems for the fetus.
Myasthenia gravis, which causes muscle weakness, does not usually cause serious or permanent complications during pregnancy. However, very rarely during labor, women who have myasthenia gravis may need help with breathing (assisted ventilation). The antibodies that cause this disorder can cross the placenta. So about one of five babies born to women with myasthenia gravis is born with the disorder. However, the resulting muscle weakness in the baby is usually temporary, because the antibodies from the mother gradually disappear and the baby does not produce antibodies of this type.
Idiopathic thrombocytopenic purpura can cause bleeding problems in pregnant women and their babies. If not treated during pregnancy, the disorder tends to become more severe. Corticosteroids, usually prednisone
given by mouth, can increase the platelet count and
improve blood clotting in pregnant women with this disorder. However, prednisone
increases the risk that the fetus will not grow as much as expected or will be born prematurely. High doses of gamma globulin may be given intravenously shortly before delivery. This treatment temporarily increases the platelet count and improves blood clotting. As a result, labor can proceed safely, and women can have a vaginal delivery without uncontrolled bleeding. Pregnant women are given platelet transfusions only when delivery by a cesarean section is needed or when the platelet count is so low that severe bleeding may occur. Rarely, when the platelet count remains dangerously low despite treatment, the spleen, which normally traps and destroys old blood cells and platelets, is removed. The best time for this surgery is during the 2nd trimester.
The antibodies that cause the disorder may cross the placenta to the fetus, resulting rarely in a dangerously low platelet count before and immediately after birth. The baby may then bleed during labor and delivery and may, as a result, be injured or die, especially if bleeding occurs in the brain. The antibodies disappear within several weeks, and the baby's blood then clots normally.
Rheumatoid arthritis does not affect the fetus, but delivery may be difficult for women if arthritis has damaged their hip joints or lower (lumbar) spine. The symptoms of rheumatoid arthritis may lessen during pregnancy, but they usually return to their original level after pregnancy.
Fibroids: Fibroids in the uterus (see Fibroids), which are relatively common noncancerous tumors, may increase the risk of preterm labor, abnormal presentation of the fetus, a mislocated placenta (placenta previa), and repeated miscarriages. Rarely, fibroids interfere with the movement of the fetus through the vagina during labor.
Cancer: Because cancer tends to be life threatening and because delays in treatment may reduce the likelihood of successful treatment, cancer is usually treated the same way whether women are pregnant or not. Some of the usual treatments (surgery, chemotherapy drugs, and radiation therapy) may harm the fetus. Thus, some women may consider abortion. However, treatments can sometimes be timed so that risk to the fetus is reduced.
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