In a 26‑week pregnant woman with a pathogenic FBN1 mutation confirming Marfan syndrome, what is the next step in management?

Management of Confirmed Marfan Syndrome at 26 Weeks Gestation

The immediate next step is to obtain urgent transthoracic echocardiography to measure the aortic root diameter, initiate beta-blocker therapy (metoprolol or propranolol) targeting heart rate 60-70 bpm, and establish monthly echocardiographic surveillance until delivery. 1, 2

Immediate Diagnostic Evaluation

The aortic root diameter is the single most critical determinant of maternal risk and will dictate all subsequent management decisions. 1, 2

• Obtain transthoracic echocardiography within 24-48 hours to measure aortic dimensions at multiple levels: annulus, sinuses of Valsalva, sinotubular junction, and ascending aorta. 1, 2
• Perform complete aortic imaging with MRI (without gadolinium) to evaluate the entire aorta beyond the root, as dilatation may extend to the arch or descending aorta. 1, 2
• Avoid CT imaging to prevent ionizing radiation exposure to the fetus. 1

Risk Stratification Based on Aortic Root Diameter

The measured aortic root diameter determines pregnancy continuation versus termination:

• Aortic root <4.0 cm: Risk of dissection is approximately 1%. Continue pregnancy with close monitoring. 1, 2
• Aortic root 4.0-4.5 cm: Risk of dissection is approximately 10%. Pregnancy continuation is controversial but may proceed with intensive surveillance. 1
• Aortic root ≥4.5 cm: Extremely high risk. Strongly consider pregnancy termination with urgent aortic root replacement. 1, 2

Medical Management

Initiate beta-blocker therapy immediately regardless of aortic diameter:

• Metoprolol or propranolol are the preferred agents due to robust safety data in pregnancy. 2
• Target heart rate 60-70 bpm to reduce aortic wall shear stress. 1, 2
• Beta-blockers reduce the rate of aortic dilatation and may improve survival. 1, 2
• Continue beta-blocker therapy throughout pregnancy and postpartum. 1

Critical contraindication: ACE inhibitors and angiotensin receptor blockers are absolutely contraindicated due to fetal toxicity. 1, 2

Surveillance Protocol

Monthly or bimonthly echocardiographic measurements of ascending aortic dimensions are mandatory until delivery to detect progressive dilatation. 1

• More frequent imaging (every 2-4 weeks) is warranted if the aortic root is ≥4.0 cm or if any interval growth is detected. 2
• Strict blood pressure control to prevent Stage II hypertension (systolic <120 mmHg). 1

Genetic Counseling and Fetal Assessment

• Provide genetic counseling immediately: Marfan syndrome is autosomal dominant with 50% transmission risk to offspring. 2
• Perform fetal echocardiography at 19-22 weeks to screen for congenital heart disease (occurs in 2-16% of offspring). 2
• Discuss options for postnatal genetic testing using cord blood or buccal swab, which avoids the 1% miscarriage risk of prenatal testing. 1

Delivery Planning

Delivery mode depends on final aortic root diameter at term:

• Aortic root <4.5 cm: Vaginal delivery is acceptable with expedited second stage (forceps or vacuum assistance). Position the patient in left lateral or semi-erect position to minimize aortic stress. Epidural anesthesia provides optimal blood pressure control. 1, 2
• Aortic root ≥4.5 cm: Cesarean delivery is advised to avoid hemodynamic stress of labor. 1, 2

Critical Pitfalls to Avoid

• Do not delay echocardiography based on absence of symptoms: Thoracic aortic disease is typically asymptomatic until catastrophic dissection occurs. 2
• Do not assume safety based on small aortic diameter alone: Approximately 15% of dissections occur at diameters <5.0 cm. 2
• Do not underestimate third trimester risk: Dissection and rupture are most likely during the third trimester and peripartum period when hemodynamic stress peaks. 1, 2
• Recognize that poor wound healing is a feature of Marfan syndrome: Sutures should be left in longer than normal postpartum, and antibiotic coverage should be extended. 1

Multidisciplinary Team Assembly

Establish immediate consultation with:

• Maternal-Fetal Medicine for high-risk pregnancy management 3, 4
• Cardiology for aortic surveillance and medical management 4, 5
• Cardiothoracic surgery for surgical planning if aortic diameter is concerning 4, 5
• Anesthesia for delivery planning, particularly regarding epidural safety in the setting of potential dural ectasia 1
• Medical genetics for counseling and fetal assessment 4

Emergency Preparedness

Develop a crisis plan for acute aortic dissection:

• If Type A dissection occurs in the third trimester, urgent cesarean section followed by aortic repair offers the best survival for both mother and fetus. 1, 6
• Maintain beta-blocker therapy and strict blood pressure control (systolic 100-120 mmHg) if dissection is diagnosed. 6