Obesity in Pregnancy

Introduction

• Obesity is one of the most common comorbidities in pregnancy, affecting over one-third of women of reproductive age in the United States.
• In the United States, approximately 40% of adults are classified as obese, with Class III obesity affecting 9.5% of adults.²
• The anesthetic implications of obesity in pregnancy are substantial and include altered airway anatomy, pharmacokinetics, increased neuraxial failure rates, and surgical challenges during cesarean delivery.
• Maternal obesity is associated with a significantly elevated risk of anesthesia-related maternal mortality: obese parturients have been noted to have 2-7 times higher risk compared with their non-obese counterparts.¹
• Management of these patients requires early planning, careful risk stratification, and close coordination between obstetricians, anesthesiologists, maternal-fetal medicine specialists, and neonatology teams.
• Patients with Class III obesity are at most significant risk for preeclampsia, gestational diabetes, macrosomia, and unplanned cesarean delivery.

Cardiopulmonary Effects

• Obese parturients have an exaggerated increase in cardiac output and blood volume. Each 100g of adipose tissue increases cardiac output by approximately 30–50 mL/min, contributing to an overall hyperdynamic circulation and an expanded blood volume.⁴
• Left ventricular hypertrophy is common secondary to volume overload and myocardial remodeling, with potential for diastolic dysfunction due to reduced compliance.
• Obese parturients have an increased incidence of hypertensive disorders of pregnancy and peripartum heart failure. In women with underlying cardiac disease, obesity is associated with higher rates of major cardiac events during pregnancy.¹
• BNP levels may be elevated, but are not always indicative of heart failure in pregnancy.⁴
• Oxygen consumption related to work of breathing is increased due to the increased chest wall weight seen in obesity and worsened in pregnancy.
• Obstructive sleep apnea (OSA) is estimated to be found in upwards of 20% of obese parturients, leading to hypercarbia and hypoxemia.⁴
• Oxygen desaturation occurs more rapidly due to a greater decrease in functional residual capacity (FRC), decreased chest wall and lung compliance, and increased airway resistance.
• Maternal obesity compounds the reduction in FRC, reduces oxygen reserve, increases O₂ consumption and CO₂ production, and predisposes to pulmonary hypertension in the context of untreated OSA/obesity hypoventilation syndrome.
• These impaired respiratory mechanics and shortened time to desaturation further worsen in the supine position.
• Just as in the non-pregnant patient, OSA may lead to metabolic disturbances increasing the risk of other comorbidities like diabetes, hypertension, and pulmonary hypertension.

Airway Challenges

• Airway management in obese pregnant patients is high-risk due to reduced FRC, increased oxygen consumption, and pharyngeal soft tissue hypertrophy.⁴
• Mallampati scores tend to worsen with weight gain and gestation, and class IV airways are more frequent in obese parturients.
• Appropriate positioning with the utilization of a ramp to improve the laryngeal view.
• Preoxygenation is vital. The time to desaturation is less in a pregnant patient compared to a non-pregnant patient, and this difference is more exaggerated in an obese patient. Consider apneic oxygenation as an adjunct.
• Nasal intubation should be avoided at any gestational age, given engorgement of pharyngeal vessels.
• Video laryngoscopy is recommended for the first attempt. Consider awake intubation for suspected difficult airways. In an emergency, have a low threshold to call for help and for early insertion of a second-generation supraglottic airway.⁵

Neuraxial Anesthesia Considerations

• Neuraxial placement is often more technically challenging in obese patients.
  • Palpation of the spinous processes and identification of the midline is difficult due to increased adiposity and depth
  • Greater incidence of “false loss” and unintentional dural puncture
• Ultrasound guidance improves identification of the midline and interspinous space and is relatively accurate at determining epidural space depth.⁷
  • Recent literature suggests higher first-pass success and shorter “needle time,” but equivalent total procedural time.⁷
• Failure rates for epidural placement, adequate analgesia, and need for epidural replacement are higher in Class III obese patients.⁶
• Early epidural placement is emphasized as a key teaching point by the Society for Obstetric Anesthesia and Perinatology (SOAP) to reduce the need for emergent general anesthesia in obese parturients
• Average depth to the epidural space increases linearly with BMI and can exceed 9 cm in patients with BMI > 50 kg/m².

Cesarean Delivery and Hemorrhage

• Cesarean delivery is more common in obese parturients due to higher rates of labor dystocia and macrosomia.
• Longer incision-to-delivery times and increased surgical difficulty are expected.
• Delays in securing airway and achieving surgical exposure may further lead to prolonged decision-to-delivery intervals.¹
• Regardless of anesthetic choice, patient should be placed in a ramped position to facilitate potential intubation if it becomes necessary.
• Aspiration prophylaxis with oral sodium citrate and an H2-blocker should be used.
• While a spinal anesthetic can be used, a combined spinal epidural technique is more commonly utilized given likelihood of longer surgical times.
• EBL is higher due to longer operative times and increased difficulty with exposure and obtaining hemostasis.
• Obese patients (BMI ≥ 40 kg/m²) are at significantly greater risk for postpartum hemorrhage, with EBL increasing by 300–600 mL compared to non-obese parturients.⁸

Postpartum and Neonatal Outcomes

• Obese parturients have higher rates of postpartum hemorrhage, wound infection and dehiscence, venous thromboembolism (VTE), and delayed recovery.¹
• Due to a 400-500% increased risk of postpartum VTE in obese parturients, both the American College of Obstetrics and Gynecology and the Society for Obstetric Anesthsia and Perinatology recommend early VTE prophylaxis.²
  • Intraoperative mechanical prophylaxis and early mobilization should be considered for all patients.
  • Pharmacologic prophylaxis should be considered for patients with additional risk factors; no BMI cutoff is present in guidelines.
• In cases of cesarean delivery, neuraxial morphine is commonly used along with a multimodal analgesic regimen including acetaminophen and NSAIDs.
• Neonates are at increased risk of macrosomia, shoulder dystocia, NICU admission, and congenital anomalies.