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Risk Factors for High-Risk Pregnancy

By Raul Artal, MD, Professor and Chair, Department of Obstetrics, Gynecology and Women's Health, Saint Louis University School of Medicine

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Some risk factors are present before women become pregnant. These risk factors include

Other problems that increase risk can develop during pregnancy or during labor and delivery.

Needing to have surgery, particularly abdominal surgery, during pregnancy increases the risk of preterm labor and miscarriages, especially early in pregnancy. Thus, surgery is usually delayed if possible. However, if necessary, surgery should proceed without delay and is still usually reasonably safe.

Physical Characteristics

The following characteristics of women affect risk during pregnancy.

Age

About 13% of all pregnancies occur in adolescents. These girls are at increased risk of having the following:

Adolescent girls can have babies who are born underweight (small for gestational age)

Part of the reason for these risks is that adolescents are less likely to get medical care during pregnancy. Thus, they may not understand what activities and behaviors (such as smoking, drinking alcohol, and having sex without using a condom) can put their pregnancy at risk. Many adolescents smoke, and they have a higher risk of getting a sexually transmitted disease. Using condoms can help prevent sexually transmitted diseases.

Women aged 35 and older are at increased risk of having the following:

Weight

Women who are very thin—with a body mass index (BMI) 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

Overweight women (with a BMI of 25 to 29.9 before pregnancy) and obese women (with a BMI of more than 30) are more likely to have the following problems:

Height

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. Also, short women are more likely to have preterm labor and a baby who are born underweight (small for gestational age).

Reproductive abnormalities

Structural abnormalities in the uterus or cervix increase the risk of the following:

Structural abnormalities include a double uterus, fibroids in the uterus, and a weak (incompetent) cervix (cervical insufficiency) 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 may be 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 any of the following:

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. 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 increases the risk of the following:

Disorders Present Before Pregnancy

Before becoming pregnant, women may have a disorder that can increase the risk of problems during pregnancy. These disorders include

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).

Disorders During Pregnancy

During pregnancy, a problem may occur or a disorder may develop to make the pregnancy high risk.

Some disorders are related to (are complications of) pregnancy. Other disorders are not directly related to pregnancy (see Overview of Disease During Pregnancy). 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. 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.

Exposures During Pregnancy

During pregnancy, being exposed to the following can increase the risk of having a baby with a birth defect:

These substances and conditions are called teratogens.

Birth defects are most likely to result if women are exposed to a teratogen 2 to 8 weeks after they become pregnant (4 to 10 weeks after their last menstrual period) because the fetus's organs are forming during this time. The risk of having a miscarriage is also increased.

Infections that are particularly dangerous during pregnancy include

Drugs that may increase the risk of birth defects include

Exposure to high temperatures (for example, in a sauna) during the 1st trimester has been linked to the development of spina bifida.

Mercury in seafood

Consuming too much mercury in seafood may harm the fetus. However, seafood contains nutrients that are important for growth and development of the fetus and breastfed infants. Thus, the Food and Drug Administration (FDA) recommends the following for women who are pregnant, who may become pregnant, or who are breastfeeding:

  • Do not eat tilefish from the Gulf of Mexico, shark, swordfish, big-eye tuna, marlin, orange roughy, and king mackerel.

  • Limit the amount of albacore tuna eaten to 4 ounces (one average meal) a week.

  • Before eating fish caught in local lakes, rivers, and coastal areas, check local advisories about the safety of such fish, and if mercury levels in the fish are not known to be low or if no advice is available, limit the amount eaten to 4 ounces (one average meal) a week and do not eat other high-mercury seafood during that week.

  • Each week, eat 8 to 12 ounces (2 or 3 average meals) of a variety of seafood that is lower in mercury.

Seafood that is lower in mercury includes flounder, shrimp, canned light tuna, salmon, pollock, tilapia, cod, and catfish (see Fish: What Pregnant Women and Parents Should Know). Some authorities (Consumer Reports: Choose the Right Fish To Lower Mercury Risk Exposure) advise against eating any tuna during pregnancy.

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