What are the maternal and fetal risks associated with pregnancy in a 31‑year‑old woman with a Fontan operation (Fontan circulation) for hypoplastic left heart syndrome (HLHS)?

Pregnancy Risk in Fontan Circulation with HLHS

Pregnancy in a woman with Fontan circulation for hypoplastic left heart syndrome carries extremely high maternal and fetal risks, and if she is currently pregnant, pregnancy termination should be discussed given the significant risk of maternal mortality and severe morbidity. 1

Maternal Risks

Mortality and Severe Morbidity

While the 2018 AHA/ACC guidelines do not explicitly list Fontan physiology under WHO Class IV conditions (which include PAH, severe ventricular dysfunction, and severe left heart obstruction), the guidelines specifically identify Fontan physiology as high-risk for thromboembolic events and warrant specialized multidisciplinary management 1. The ESC guidelines from 2011 show that Fontan patients have elevated miscarriage rates compared to other congenital heart disease populations 2.

Recent meta-analysis data from 2025 reveals more encouraging maternal outcomes than previously thought, with no maternal mortality reported among 400 pregnant women with Fontan circulation across 1260 pregnancies 3. However, significant complications remain common:

• Arrhythmias occur in 6.59% of pregnancies (all supraventricular tachycardia) 3
• Heart failure develops in 3.71% of cases 3
• Cardiac decompensation requiring hospitalization occurs in approximately 50% of pregnancies 4
• Postpartum hemorrhage risk is 4.28 times higher than in women without Fontan circulation 5
• Severe maternal morbidity is 6.09 times higher overall 5

Cardiovascular Deterioration

Medium-term functional outcomes show concerning trends: ejection fraction declines significantly more post-pregnancy compared to matched male controls, and mean VO2max decreases after pregnancy 4. However, worsening NYHA class is relatively uncommon (15.4%), suggesting that acute pregnancy complications don't necessarily translate to long-term functional limitation 4.

Thrombotic Risk

Fontan physiology creates a prothrombotic state due to chronic low cardiac output and abnormal flow dynamics. The AHA/ACC guidelines explicitly contraindicate estrogen-containing contraceptives in these patients due to thromboembolism risk 1. During pregnancy, the hypercoagulable state compounds this baseline risk.

Fetal and Neonatal Risks

Prematurity

Preterm delivery is the predominant fetal complication, occurring in 57.31% of pregnancies 3. Other studies confirm this, with 90% of live births being premature in one cohort 6 and 43% prematurity rate in another 7.

Fetal Growth and Mortality

• Intrauterine growth restriction affects 23% of all pregnancies and 50% of live births 6
• Neonatal mortality is 4.38%, primarily from complications of prematurity 3
• Live birth rate is only 46.7%, with miscarriage rate of 53.3% in some series 7

Congenital Heart Disease Recurrence

Offspring have increased risk of CHD, warranting fetal echocardiography 1. The exact recurrence rate for HLHS specifically is not provided in the guidelines, but prepregnancy counseling should address this risk.

Management Approach If Pregnancy Occurs

Multidisciplinary Team Requirements

Management must involve ACHD specialists, maternal-fetal medicine, anesthesiology, and hematology 1. Single-center data shows successful outcomes are possible with close monitoring, but only in highly selected patients 7.

Specific Monitoring Needs

• Serial echocardiography throughout pregnancy 7
• Vigilance for volume shifts, arrhythmias, and heart failure 1
• Antithrombotic therapy individualization (aspirin used in 62.5% of one cohort) 7
• Avoid warfarin during pregnancy due to teratogenicity; transition to alternative anticoagulation if needed 1

Delivery Planning

• Cesarean section is common (85.7% in one series) 7, though the AHA/ACC guidelines note that most women with CHD do not require cesarean delivery for cardiac reasons alone 1
• Delivery should occur at a tertiary center with ACHD expertise
• Anesthesia planning is critical given risks with general anesthesia 2

Postpartum Considerations

Cardiac complications occur in approximately 28.6% postpartum, including transient heart failure and thromboembolism 7. The ESC guidelines note that maternal death in pulmonary hypertension (a related high-risk condition) occurs in the last trimester and first months postpartum 2, emphasizing the need for extended postpartum monitoring.

Critical Counseling Points

Before any pregnancy attempt:

• Comprehensive prepregnancy counseling is mandatory 1
• Cardiopulmonary exercise testing can predict maternal and neonatal outcomes 1
• Discussion of contraceptive options (progesterone-only methods, IUDs, or permanent sterilization—never estrogen-containing contraceptives) 1
• Frank discussion about the 53% miscarriage rate and high prematurity risk
• Consideration of partner vasectomy given patient's long-term prognosis 1

If currently pregnant:

• Pregnancy termination should be offered and discussed, performed at a tertiary center experienced in managing complex cardiac patients 2
• If patient chooses to continue, acknowledge this is feasible in selected cases but requires intensive monitoring and acceptance of substantial risks

The evidence shows pregnancy outcomes in Fontan circulation have improved compared to historical data, but risks remain substantial and significantly exceed those of normal pregnancy.