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:
Many women with complex high-risk condition benefit from treatment at a specialized center that provides care for by doctors who specialize in high-risk pregnancies.
Maternal mortality
Maternal mortality refers to the death of women when death is caused by complications of pregnancy and childbirth.
In the United States, 19 women died for every 100,000 deliveries in 2017. In the United States, almost half of pregnancy-related deaths occur in black women. The maternal mortality rate is higher in the United States than in other Western countries, such as the following:
However, almost all maternal deaths occur in developing countries. Over two thirds occur in sub-Saharan Africa (including Nigeria), and almost one fifth occur in South Asia (including India).
Comparing Mortality Ratios for Mothers in Different Countries
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In this graph, the maternal mortality ratios in different countries are compared. Maternal mortality refers to the number of women who die because of problems related to pregnancy and who die during pregnancy, during delivery, or soon after delivery. The maternal mortality ratio is the number of such deaths for every 100,000 live births (delivery of a living baby). In 2017, ratios ranged from 2 (Poland) to 1,150 (South Sudan) deaths per 100,000 live births (these countries are not shown below). The maternal mortality ratio is higher in the United States (19 per 100,000 live births) than in most other Western countries. Data from the World Health Organization, United Nations Children’s Fund (UNICEF), United Nations Population Fund (UNFPA), The World Bank, and the United Nations Population Division. Trends in Estimates of Maternal Mortality: 2000–2017. Geneva, World Health Organization, 2019. 
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The maternal death rate varies greatly by race and ethnicity worldwide. In the United States, the maternal death rate is over 3 times higher in black women and 2.5 times higher in American Indian and Alaska native women than in white women. In Brazil, the maternal mortality is about 5 times higher in women of African descent than in white women. In the United Kingdom, it is many times higher in black women than in white women.
The most common causes of death in pregnant women are
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Bleeding (hemorrhage), which accounts for over one fourth of deaths
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High blood pressure, including preeclampsia (a type of high blood pressure that develops during pregnancy)
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Sepsis (a serious bodywide response to an infection)
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An abnormally located pregnancy (ectopic pregnancy)—that is, one not in its usual location in the uterus
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Disorders that women had before they became pregnant (such as obesity and infectious diseases, including HIV infection)
Problems that contribute to deaths in pregnant women include
About 3 of 5 of maternal deaths could be prevented.
Perinatal mortality
Perinatal mortality refers to the death of fetuses and newborns that occur around the time of delivery. In the United States, the perinatal mortality rate is 6 to 7 deaths per 1,000 deliveries.
The most common causes of death in fetuses and newborns are
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Disorders in the mother, such as high blood pressure, diabetes, obesity, or an autoimmune disorder
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Infections
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Abnormalities in the placenta—one that detaches too soon (placental abruption) or is mislocated (placenta previa)
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Genetic abnormalities in the fetus
Risk Assessment During Pregnancy
Certain conditions or characteristics, called risk factors, make a pregnancy high risk. As part of routine care during pregnancy, doctors check for these factors to determine the degree of risk for a particular woman and baby and thus to provide better medical care. Genetic evaluation is particularly important. It involves assessing the couple’s family history and, if needed, analyzing blood or tissue samples (such as cells from the inside of the cheek). This evaluation is done to determine whether a couple is at increased risk of having a baby with a hereditary genetic disorder.
Factors that can affect risk in women include
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Physical characteristics (such as age and weight)
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Social characteristics (such as marital status)
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Disorders that were present before pregnancy, such as chronic high blood pressure (hypertension), diabetes, sexually transmitted diseases, or kidney infections
High-risk pregnancies must be closely monitored, and sometimes women are referred to a center that specializes in managing these pregnancies.
The most common reasons for referral before delivery are
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Preterm labor (often due to premature rupture of the membranes)
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Disorders that were present before or that develop during the pregnancy, such as diabetes, high blood pressure, and severe (morbid) obesity
