Fainting (Syncope) During Pregnancy

What is syncope? Syncope is a brief loss of consciousness and postural change often caused by a brief decrease in blood flow to the brain.

How common is syncope (AKA "fainting" or "loss of consciousness") during pregnancy? Approximately 4.6% of women suffer from at least one episode of syncope during pregnancy. 28.2% of women interviewed reported a pre-syncopal episode including the symptoms of dizziness, lightheadedness, nausea, sweating and potentially collapsing to the floor.

What causes syncope? During pregnancy women's veins dilate in response to increased hormones from the placenta. This in turn causes a pooling effect that causes a decrease in cardiac output and a decrease in blood pressure. In susceptible individuals the vagus nerve is then stimulated causing a "paradoxical" (i.e. counter-intuitive) reaction of yet-again increased vein dilation and a slowing of the heart. In essence, in the pregnant woman's body this can occur due to the body trying to compensate for what appears to be a loss of blood. This is the cause of fainting 99% of the time.

What else can cause syncope? 1% of the time syncope can be due to more serious conditions such as heart disease, brain tumors, blood clots, seizures, abnormal heart beat, low blood sugar and other blood chemistry abnormalities.

What tests should be done? Start with a history and physical exam by a health professional. You may be asked to list the symptoms you had before the episode: palpitations, shortness of breath, chest pain, lightheadedness. Were you hydrated well? How long did the episode last? Did you injure yourself when you fell? The physical exam may include vital signs, heart and neurological exam. Some physicians may get an EKG if they believe your heart may be involved. Many times, there is no need for additional testing. In the rare instance that something more serious than a vagal response is considered, your health care provider may order blood tests, additional heart monitoring or consultations from other health professionals.

What is the prognosis for the fetus and should additional testing be done? The prognosis for the fetus is excellent. In general, no additional testing is necessary.

What general recommendations do we make to pregnant patients with a history of syncope? Get up slowly when changing positions. If you must stand for a prolonged period of time, make sure to move your legs. Remain well hydrated. Eat regular meals to maintain a steady blood sugar. Identify your syncopal triggers and avoid them. If symptoms persist, see your health care provider. The condition will most likely resolve after delivery.

Reference: Yarlagadda S, Poma PA, Green LS, Katz V. Syncope during pregnancy. Obstetrics and Gynecology. 2010; 115(2)377-80.