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 following characteristics of women affect risk during pregnancy.

Age: 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 preterm labor and anemia. They are more likely to have babies who have anemia or who are underweight (small for gestational age).

Women aged 35 and older are at increased risk of problems such as high blood pressure, gestational diabetes (diabetes that develops during pregnancy), chromosomal abnormalities in the fetus, and stillbirth. Also, they are more likely to have complications during labor such as preeclampsia, a placenta that detaches too soon (placental abruption) or is mislocated (placenta previa), and difficult labor.

Weight: 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, high blood pressure, or preeclampsia. They are more like to have a pregnancy that lasts 42 weeks or longer (postterm) and to need a cesarean delivery.

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 (see Complications of Labor and Delivery: Shoulder Dystocia). Also, short women are more likely to have preterm labor and a baby who has not grown as much as expected.

Reproductive Abnormalities: 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 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 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)

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 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 Complications of Pregnancy: Placenta Previa).

Disorders Present Before Pregnancy

Before becoming pregnant, women may have a disorder that can increase the risk of problems during pregnancy (see Pregnancy Complicated by Disease). 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).

Last full review/revision December 2008 by Christian M. Briery, MD; John Morrison, MD