A pregnancy is considered high risk when the health of the mother, the baby, or both faces a greater chance of complications than in the general population. Roughly 20 to 30 percent of pregnancies fall into this category worldwide. There is no single checklist that every hospital uses. The label can come from a condition you had before getting pregnant, something that develops during pregnancy, your age, your weight, or carrying more than one baby.
Pre-existing Health Conditions
Certain chronic conditions raise your risk from the very start of pregnancy. The most common ones are diabetes (type 1 or type 2), chronic high blood pressure, heart disease, autoimmune conditions like lupus, kidney disease, and thyroid disorders. For women with diabetes, high blood sugar around the time of conception increases the chance of birth defects and other health problems for the baby. Chronic high blood pressure, meaning blood pressure that was elevated before pregnancy or before 20 weeks, raises the risk of preterm delivery, low birth weight, and stroke.
Heart conditions deserve special attention. Many women with heart disease do have healthy pregnancies, but the extra blood volume and cardiac workload of pregnancy can push an already compromised heart into dangerous territory. Women with a history of blood clotting disorders, epilepsy, or severe mental health conditions also typically receive closer monitoring throughout pregnancy.
Conditions That Develop During Pregnancy
Some high-risk conditions only appear once you’re already pregnant. The two most significant are gestational diabetes and preeclampsia.
Gestational diabetes is glucose intolerance diagnosed for the first time during pregnancy. It usually shows up in the second or third trimester and is caught through routine glucose screening. Left unmanaged, it can lead to an overly large baby (over 4 kg, or about 8.8 pounds), birth injuries, and blood sugar problems in the newborn.
Preeclampsia is new-onset high blood pressure (140/90 or higher) developing at or after 20 weeks of pregnancy, combined with signs of organ stress such as protein in the urine, liver problems, or changes in blood clotting. It can progress rapidly and, in severe cases, lead to seizures (eclampsia) or organ failure. The only definitive treatment is delivering the baby, which sometimes means an early delivery if the condition becomes dangerous.
Maternal Age
Advanced maternal age has historically been defined as 35 years or older at the estimated delivery date. The American College of Obstetricians and Gynecologists still uses this threshold, though the risks are better understood as a continuum: they increase gradually with each year rather than jumping sharply at 35. More recent research breaks it into five-year increments (35 to 39, 40 to 44, 45 to 49, and 50 and older) to reflect how significantly risk can differ even within the “over 35” group.
The original concern behind the age cutoff was declining fertility and a rising chance of chromosomal abnormalities, particularly Down syndrome. Data from the FASTER trial and the National Birth Defects Prevention Study confirmed a significant association between chromosomal abnormalities and births to women 35 and older. But age also correlates with higher rates of gestational diabetes, preeclampsia, miscarriage, and cesarean delivery. Very young mothers, typically under 17, face elevated risks as well, including preterm birth and low birth weight.
Body Weight Before Pregnancy
Your weight at the time of conception plays a measurable role. A pre-pregnancy BMI in the ideal range is 20 to 24.99. A BMI over 25 is associated with greater difficulty conceiving and higher rates of miscarriage and stillbirth. A BMI over 30 (the threshold for obesity) raises those risks further and adds complications during labor, including a higher likelihood of cesarean delivery. Being underweight (BMI below 18.5) carries its own set of risks, including preterm birth and having a baby with low birth weight.
These aren’t just statistical associations. Excess weight changes how the body handles blood sugar and blood pressure, which feeds directly into the gestational diabetes and preeclampsia risks described above. It also affects anesthesia during delivery and wound healing afterward.
Carrying Multiples
Twin, triplet, and higher-order pregnancies are automatically classified as high risk. Over 60 percent of twins and nearly all higher-order multiples are born before 37 weeks. Premature babies often weigh less than 2,500 grams (about 5.5 pounds) and may need help breathing, eating, regulating body temperature, and fighting infection.
Women carrying multiples are more than twice as likely to develop pregnancy-related high blood pressure and more than twice as likely to become anemic. Their babies face about double the risk of congenital abnormalities, including heart defects and neural tube defects like spina bifida. After delivery, the large placental area and overstretched uterus increase the chance of postpartum hemorrhage.
Identical twins who share a placenta face an additional risk called twin-to-twin transfusion syndrome, where blood vessels in the shared placenta divert blood unevenly between the two babies. This occurs in about 15 percent of identical twins with a shared placenta and requires close ultrasound monitoring.
Placental and Cervical Problems
The placenta’s position matters. In placenta previa, the placenta attaches low in the uterus and partially or completely covers the cervix. This can cause severe bleeding, particularly in the third trimester, and almost always requires a cesarean delivery. In some cases, the placenta shifts upward as the uterus grows, resolving the problem on its own. When it doesn’t, close monitoring is needed to watch for sudden hemorrhage that could require an emergency delivery before full term.
A short or weakened cervix (sometimes called cervical insufficiency) is another structural risk factor. The cervix may begin to open too early in pregnancy without contractions, leading to second-trimester loss or very premature birth. It’s often detected through ultrasound measurements and may be treated with a cervical stitch or progesterone supplementation.
Fetal Growth Problems
When a baby is growing more slowly than expected, the condition is called fetal growth restriction. It’s typically flagged when the baby’s estimated weight falls below the 10th percentile for their gestational age, especially when ultrasound also shows signs that the placenta isn’t delivering enough blood and nutrients. In more severe cases, the baby’s weight drops below the 3rd percentile.
Growth restriction can result from placental problems, maternal high blood pressure, infections, or genetic factors. It increases the risk of stillbirth, so pregnancies with this diagnosis involve frequent ultrasounds and monitoring of blood flow through the umbilical cord. Delivery may be scheduled early if the baby shows signs of distress or if growth stalls entirely.
Obstetric History
What happened in a previous pregnancy often shapes the risk profile of the next one. A history of preterm birth, cesarean delivery, miscarriage, or stillbirth all raise the level of concern. Women who experienced preeclampsia in an earlier pregnancy have a significantly higher chance of developing it again. A prior cesarean delivery affects how the placenta may implant in future pregnancies and influences decisions about delivery method.
Past gynecological conditions also factor in. Uterine fibroids, ovarian cysts, or a history of uterine or cervical surgery can all change how the uterus accommodates a growing pregnancy. Even a history of drug allergies is flagged during early prenatal visits because it affects what medications are safe to use if complications arise.
What High-Risk Monitoring Looks Like
Being labeled high risk doesn’t mean something will go wrong. It means your care team will watch more closely. In practice, that usually means more frequent prenatal visits, additional ultrasounds to track the baby’s growth and the placenta’s position, and blood work or urine tests to catch complications early. You may be referred to a maternal-fetal medicine specialist, a doctor who focuses specifically on complicated pregnancies, either for a one-time consultation or for ongoing co-management alongside your regular provider.
The experience varies widely depending on the reason for the classification. Someone with well-controlled type 1 diabetes may simply have a few extra appointments and an earlier delivery date. Someone with severe preeclampsia might be hospitalized for days or weeks of monitoring. The common thread is that identifying risk early gives your care team the best chance to intervene before a complication becomes an emergency.