How is high risk classified in Obstetrics (OB) and Gynecology (GYN)?

High-Risk Pregnancy Classification in Obstetrics and Gynecology

High-risk pregnancy is defined as any pregnancy in which the woman, fetus, or infant faces increased risk of death or residual injury requiring additional resources, procedures, or specialized care to optimize outcomes. 1

Core Definition and Framework

A high-risk pregnancy encompasses any unexpected or unanticipated medical or obstetric condition with actual or potential hazard to maternal or fetal health and well-being. 2 The classification is not absolute—risk perception may differ between the woman and her healthcare provider, making continuous reassessment essential throughout the reproductive lifespan. 3

Major Risk Categories

Medical Comorbidities

The following preexisting conditions significantly elevate pregnancy risk:

• Cardiovascular disease, including rheumatic heart valve disease, Marfan syndrome, and Ehlers-Danlos syndrome 1
• Hypertensive disorders, including chronic hypertension (particularly systolic ≥160 mm Hg or diastolic ≥100 mm Hg) and preeclampsia 3, 1
• Diabetes mellitus, both pregestational and gestational 1
• Thrombophilia and history of venous thromboembolism, particularly with personal history of unprovoked or estrogen-related VTE, family history, or known thrombophilia (Factor V Leiden, prothrombin gene mutation, protein S/C deficiency, antithrombin deficiency, antiphospholipid syndrome) 3
• Autoimmune conditions including systemic lupus erythematosus 3
• Thyroid disorders 4

Obstetric Risk Factors

• Previous adverse pregnancy outcomes, including prior preterm birth, preeclampsia, gestational diabetes, or placental complications 1, 4
• Multiple gestation 1
• Prior cesarean delivery, particularly multiple cesareans (increases risk of placenta accreta spectrum disorder) 4
• Advanced maternal age (>35 years in most guidelines, >40 years in Swedish guidelines) 3
• High parity (≥3 deliveries) 3

Lifestyle and Behavioral Factors

• Substance use, including tobacco, alcohol, cocaine, methamphetamines, and other recreational drugs 1, 4
• Obesity (BMI >30 kg/m²) 3, 5
• Smoking (>10 cigarettes/day in some classifications) 3

Socioeconomic and Geographic Factors

• Rural residence (9% higher probability of severe maternal morbidity compared to urban residents) 5
• Low socioeconomic status and lack of education (women with no education have twice the odds of high-risk pregnancy) 6
• Racial disparities: African American women have 3.2 times higher maternal mortality than white women; American Indian/Alaska Native women have 2.3 times higher risk 5

Pregnancy-Related Complications

• Preeclampsia with or without severe features 1, 7
• Superimposed preeclampsia (highest readmission rate at 6.6%) 7
• Placental abnormalities, including placenta previa, abruption, or retained placenta 4
• Fetal anomalies requiring specialized care or fetal surgery 3
• Hyperemesis gravidarum requiring hospitalization 3
• Ovarian hyperstimulation syndrome 3

Risk Stratification Timing

Prepregnancy Period

Risk assessment should begin before conception to optimize chronic medical conditions and identify modifiable risk factors. 3 Only 18-45% of high-risk women receive prepregnancy care, representing a critical gap. 3

During Pregnancy

Risk assessment must be continuous and repeated throughout pregnancy, not just at the first prenatal visit. 3 The Society for Maternal-Fetal Medicine recommends evaluating five key areas at each assessment: 3

1. Healthcare system's ability to manage the condition
2. Fetal and neonatal prognosis
3. Patient's ability to manage the condition
4. Woman's desire to continue pregnancy
5. Expertise of available healthcare practitioners

Risk increases with advancing gestational age as complications develop or medical interventions become necessary. 3

Postpartum Period

One-third of pregnancy-related deaths occur 7-365 days after delivery, and 1.8% of women are readmitted with severe maternal morbidity. 3 The majority of readmissions occur within 10 days of discharge. 7 Women with hypertensive disorders at delivery require particularly close follow-up, with evaluation for cardiovascular risk factors within 6 months to 1 year postpartum. 8

Quantitative Risk Thresholds

VTE Risk Scoring (Multiple International Guidelines)

Various international guidelines use point-based systems for VTE risk: 3

• Score 2: Moderate risk requiring 5-10 days postpartum prophylaxis
• Score 3: High risk requiring prophylaxis from 28 weeks gestation and up to 6 weeks postpartum
• Score 4: Very high risk requiring prophylaxis from conception/time of assessment

Hypertension Severity Classification

• Adequately controlled hypertension: Lower risk category 3
• Systolic 140-159 or diastolic 90-99 mm Hg: Moderate risk 3
• Systolic ≥160 or diastolic ≥100 mm Hg: High risk associated with increased adverse pregnancy events 3

Common Pitfalls in Risk Classification

Avoid single-timepoint assessment. Risk is dynamic and evolves throughout pregnancy—a woman classified as low-risk at booking may develop preeclampsia at 34 weeks, fundamentally changing her risk profile. 3

Don't overlook contextual factors. Medical risk factors alone are insufficient; socioeconomic status, geographic location, healthcare access, and implicit bias all contribute to maternal outcomes. 3 Provider-level delays in recognition, diagnosis, or referral contribute to preventable maternal mortality. 3

Recognize that "high-risk" labeling causes distress. Women report fear and anxiety after being labeled high-risk, though they do modify behaviors based on recommendations. 3 Balance honest risk communication with supportive counseling.

Prevalence Data

In India's national survey, 49.4% of pregnant women had at least one high-risk factor, with 33% having a single risk and 16.4% having multiple risks. 6 In the United States, nearly 13% of the four million annual deliveries experience one or more major complications. 9 These figures underscore that high-risk pregnancy is common, not exceptional.