What is the maximum size of a maternal cerebral aneurysm (cerebral aneurysm) that is considered safe for a pregnant woman to pursue a vaginal delivery?

Management of Maternal Cerebral Aneurysms and Vaginal Delivery

Cerebral aneurysms ≤5 mm are safe for vaginal delivery, while aneurysms >5 mm require careful risk assessment, with cesarean delivery strongly considered for aneurysms >10 mm or those with high-risk features. 1, 2

Size-Based Risk Stratification

Low-Risk Aneurysms (≤5 mm)

• Aneurysms ≤5 mm are unlikely to undergo significant growth during pregnancy and can safely pursue vaginal delivery. 2, 1
• In a retrospective series of five pregnancies with eight cerebral aneurysms, all aneurysms measuring 2-5 mm remained unchanged in size throughout pregnancy, with no subarachnoid hemorrhages occurring. 1
• These small aneurysms remain stable despite the physiologic increase in circulating blood volume during pregnancy. 1

Intermediate-Risk Aneurysms (5-10 mm)

• Aneurysms between 5-10 mm without high-risk features (blebs, irregular shape, high-risk location, or increased aspect ratio) are at low risk of rupture and unlikely to change during pregnancy. 1
• One case demonstrated a 6 mm aneurysm that increased to 7 mm during the third trimester but returned to baseline postpartum, without rupture. 1
• Vaginal delivery with assisted second stage (to minimize Valsalva maneuver) is reasonable for aneurysms in this size range without high-risk morphologic features. 2, 1

High-Risk Aneurysms (>10 mm)

• Aneurysms ≥10 mm should be strongly considered for cesarean delivery under general anesthesia to avoid hemodynamic stress from Valsalva maneuver. 2
• A case report documented successful spontaneous vaginal delivery under general anesthesia in a patient with a 10 mm aneurysm, though cesarean section was the original recommendation. 2
• The presence of a cerebral aneurysm is not an automatic contraindication to Valsalva maneuver, but larger aneurysms warrant more conservative delivery planning. 2

Critical Risk Factors Beyond Size

High-Risk Morphologic Features

Women with unrepaired coarctation of the aorta or those with residual hypertension, residual coarctation, or aortic aneurysms have increased risk of cerebral aneurysm rupture during pregnancy and delivery. 3

Timing of Rupture Risk

• Most aneurysm ruptures occur during the third trimester (77.8% of cases), when hemodynamic stress is maximal. 4
• Approximately 73% of aneurysms in pregnant patients present as ruptured rather than unruptured. 5

Delivery Management Algorithm

For Aneurysms ≤5 mm

• Proceed with vaginal delivery using standard obstetric management. 1
• Epidural analgesia is recommended to reduce pain-related sympathetic activity and minimize the urge to push. 3
• Lateral decubitus positioning during labor attenuates hemodynamic impact of uterine contractions. 3

For Aneurysms 5-10 mm Without High-Risk Features

• Plan for assisted vaginal delivery with shortened second stage to minimize Valsalva maneuver. 3, 2
• Epidural analgesia should be utilized to reduce catecholamine surge and minimize pushing efforts. 3
• Delivery should occur in a tertiary center with neurosurgical capabilities immediately available. 6

For Aneurysms >10 mm or With High-Risk Features

• Cesarean delivery should be strongly considered, potentially under general anesthesia. 2
• If vaginal delivery is attempted, it must occur in a tertiary center with immediate neurosurgical and cardiothoracic surgery availability. 6
• General anesthesia may be considered to completely eliminate Valsalva maneuver during delivery. 2

Treatment Considerations for Unruptured Aneurysms

Pre-Delivery Treatment

• Surgical management of unruptured aneurysms during pregnancy is associated with 31.9% fewer complications compared to no treatment. 4
• Coil embolization is associated with lower complication rates than surgical clipping (9.5% vs 23.1%) for ruptured aneurysms during pregnancy. 4
• Treatment decisions for unruptured aneurysms should be made on a case-by-case basis with multidisciplinary input from neurosurgery, obstetrics, and anesthesiology. 7, 5

Ruptured Aneurysm Management

• Ruptured aneurysm obliteration should be prioritized before delivery, followed by vaginal delivery or cesarean section based on obstetric indications. 7
• Combined neurosurgical-obstetrical procedures were used for 8 patients with ruptured aneurysms near term. 4

Common Pitfalls to Avoid

• Do not assume all cerebral aneurysms contraindicate vaginal delivery—size and morphology are critical determinants. 2, 1
• Do not delay treatment of ruptured aneurysms for obstetric reasons—maternal stabilization takes priority. 7
• Do not use stent-assisted coiling routinely during pregnancy—one case resulted in maternal death from a giant basilar tip aneurysm. 7
• Do not perform cesarean delivery solely for small (<5 mm) aneurysms—this increases maternal morbidity without clear benefit. 1

Postpartum Monitoring

• Hemodynamic monitoring should continue for at least 24 hours postpartum to monitor for fluid shifts that may precipitate aneurysm rupture. 8, 6
• Aneurysms that increased in size during pregnancy (such as from 6 to 7 mm) may return to baseline size postpartum. 1