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There is no formal or universally accepted definition of a high-risk pregnancy. Generally, however, a high-risk pregnancy involves at least one of the following:
Certain conditions or characteristics, called risk factors, make a pregnancy high risk. Doctors identify these factors to determine the degree of risk for a particular woman and baby and thus to provide better medical care. High-risk pregnancies must be closely monitored, and sometimes women are referred to a center that specializes in managing these pregnancies.
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. Other problems that increase risk develop during pregnancy or during labor and delivery.
The following characteristics of women affect risk during pregnancy.
Girls aged 15 and younger are at increased risk of having the following:
Women aged 35 and older are at increased risk of the following:
A preexisting disorder that increases risk during pregnancy, such as high blood pressure or diabetes
Problems related to the pregnancy such as preeclampsia, gestational diabetes (diabetes that develops during pregnancy), chromosomal abnormalities in the fetus, and stillbirth
Complications during labor, such as difficult labor or a placenta that detaches too soon (placental abruption) or is mislocated (placenta previa)
Women who are very thin (with a body mass index of less than 19.8—see Table: Determining Body Mass Index) or weigh less than 100 pounds before becoming pregnant are more likely to have small, underweight babies.
Obese women (with a body mass index of more than 29) are more likely to have very large babies, which may be difficult to deliver. Also, obese women are more likely to develop gestational diabetes, high blood pressure, or preeclampsia. They are more likely to have a pregnancy that lasts 42 weeks or longer (postterm) and to need a cesarean delivery.
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 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 uterus or cervix increase the risk of having a difficult labor, a miscarriage, or a fetus in an abnormal position and of needing a cesarean delivery. These abnormalities include a double uterus and a weak (incompetent) cervix that tends to open (dilate) as the fetus grows.
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.
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 any of the following:
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
Labor that required a cesarean delivery
A baby who died shortly before or after birth (stillbirth)
Too much amniotic fluid in the uterus (polyhydramnios)
A fetus who was in an abnormal position, such as buttocks first (breech)
A baby with an injury that stretched of the nerves in the baby's shoulder (brachial plexus injury) during delivery
A previous pregnancy with more than one fetus
A seizure disorder
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 Screening). If these women become pregnant again, tests such as high-resolution ultrasonography, chorionic villus sampling, and amniocentesis may help determine whether the fetus has a genetic disorder or birth defect. These women may be referred to a specialist.
Having had five or more pregnancies increases the risk of very rapid labor and excessive bleeding after delivery. Having had twins or more fetuses in one pregnancy (multiple births) increases the risk of a mislocated placenta (placenta previa—see Placenta Previa).
Before becoming pregnant, women may have a disorder that can increase the risk of problems during pregnancy (see Pregnancy Complicated by Disease). These disorders include high blood pressure, diabetes, kidney disorders, kidney infections, heart failure, sickle cell anemia, and sexually transmitted diseases. Women who have one of these disorders 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).
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 cause birth defects (teratogens), such as radiation, certain chemicals, drugs (see Drug Use During Pregnancy), or infections. Infections that are particularly dangerous during pregnancy include chickenpox, hepatitis, herpes simplex, rubella (German measles), syphilis, toxoplasmosis, and infections with cytomegalovirus or coxsackievirus. Or a disorder may develop. Some disorders are related to (are complications of) pregnancy. Other disorders are not directly related to pregnancy (see Pregnancy Complicated by Disease). Certain disorders are more likely to occur during pregnancy because of the many changes pregnancy causes in a woman's body.
Pregnancy complications are problems that occur only during pregnancy (see Complications of 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 pregnancy. Women who have heavy bleeding are at risk of losing the baby or of going into shock and, if not promptly treated, of dying during labor and delivery.
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