Pregnancy may increase the risk of brain aneurysms due to hormonal and cardiovascular factors that occur when pregnant, although the risk is rare.

Pregnancy causes changes in hormones, blood flow, and water retention in the body.

These may increase the risk of brain aneurysms and related complications.

This article looks at what a brain aneurysm is, risk factors, diagnosis, treatment, and outlook.

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A brain aneurysm, or cerebral aneurysm, is a weakened spot in an artery in the brain. The artery bulges out, which can put pressure on brain tissue or nerves.

If a brain aneurysm ruptures, it can bleed into the surrounding brain tissue. The medical term for this is a hemorrhage.

Any brain aneurysm can rupture. A ruptured brain aneurysm is a medical emergency and can be life threatening.

Read more about brain aneurysms.

According to a 2019 systematic review, the frequency of unruptured brain aneurysms in pregnancy is unknown, but the occurrence is rare. The frequency of ruptured aneurysms in pregnancy ranges from 3–11 per 100,000 pregnancies.

Bleeding within the skull, or intracranial bleeding, due to a ruptured brain aneurysm in pregnancy is rare.

A ruptured brain aneurysm is the most common cause of subarachnoid hemorrhage (SAH) — bleeding around the brain — during pregnancy. SAH is five times more common in pregnant people than in nonpregnant people.

Read more about brain aneurysm prevalence.

In most cases, small, unruptured aneurysms will not cause any symptoms. A larger aneurysm may cause symptoms such as:

  • pain behind and above an eye
  • numbness
  • weakness
  • facial paralysis on one side of the face
  • dilated pupil in an eye
  • changes in vision, such as double vision

Symptoms of a ruptured brain aneurysm in pregnancy may include:

Other symptoms may include:

Learn how an unruptured brain aneurysm can affect behavior.

To diagnose a brain aneurysm in pregnancy, doctors may use the following tests:

  • blood pressure test
  • blood tests, such as a complete blood count
  • lumbar puncture
  • MRI scan
  • CT scan of the skull
  • CT angiography, which combines a CT scan with a special dye to create images of blood vessels

If people receive a CT scan of the head or chest area during pregnancy, there is no risk of radiation to the fetus.

Doctors may use a CT scan during pregnancy to make a prompt or urgent diagnosis if they suspect a brain aneurysm and will take steps to protect the abdominal area.

According to a 2020 systematic review, changes in hormones and blood flow during pregnancy increase the risk of a brain aneurysm forming, as well as the risk of an aneurysm growing or rupturing.

Changes to the blood occur during pregnancy to support the developing fetus, but these changes may also increase the risk of brain aneurysms. These changes include increases in total blood volume, plasma volume, and red blood cell mass.

Cardiac output, which is the amount of blood the heart pumps out, also increases by 30–50% in pregnancy, reaching its peak in the third trimester. An increase in estrogen in pregnancy may also increase blood flow in the brain.

Pregnancy can cause water retention, which results in an increase in blood volume and cardiac output.

The third trimester and labor increase the risk of brain aneurysms in pregnancy, as the most significant changes in hormones and blood flow occur at this time. Being over the age of 30 is also a risk factor.

The risk of a ruptured brain aneurysm is higher in the third trimester and for 6 weeks after giving birth.

Black or Asian people are more likely to experience bleeding in the brain due to a ruptured brain aneurysm than white people. Having a medical history of the following conditions may also increase the risk:

A brain aneurysm can cause severe complications if it ruptures, including:

If a brain aneurysm is small and not causing symptoms, doctors may first monitor the aneurysm to assess the risk.

Treatment for a brain aneurysm in pregnancy can include surgical clipping and endovascular coiling.

For surgical clipping, a doctor will place a small metal clip onto the aneurysm to cut off its blood supply. This procedure is a type of open brain surgery, or open craniotomy.

Endovascular coiling is a less invasive procedure than surgical clipping. A doctor will insert a long tube into an artery to reach the brain aneurysm. They will then guide small springs, or coils, into the aneurysm to reduce blood flow to it.

In early pregnancy, if a person has surgical clipping of an aneurysm, the pregnancy can continue to full term with a vaginal delivery.

A diagnosis of an aneurysm in later pregnancy or severe symptoms may result in an emergency cesarean section.

Learn how to prevent a brain aneurysm.

According to the National Institutes of Health, surgical clipping is highly effective, and complete clipping of an aneurysm usually means it will not recur.

In some cases, people may need to have repeated endovascular coiling, as with this treatment method, an aneurysm may recur.

In a 2019 review, endovascular coiling resulted in successful treatment in eight cases of brain aneurysms in pregnancy, without requiring open craniotomy. Treatment occurred before delivery.

In the case of a ruptured brain aneurysm, immediate surgical treatment may help to improve outcomes.

People who do not receive treatment have a 33–50% chance of experiencing a recurring bleed in the brain, with maternal mortality rates between 50% and 68%. Surgery also helps to lower fetal mortality rates compared to receiving medication only.

Brain aneurysms and related complications in pregnancy are rare, but pregnancy does increase the risk. Body changes during pregnancy, particularly in the third trimester and postpartum period, can increase the risk.

People will need to seek immediate medical attention if they experience a sudden, severe headache, vomiting, or loss of consciousness.