Causes of Migraines in Third Trimester of Pregnancy
The primary causes of migraines in the third trimester of pregnancy include hormonal fluctuations, physiological changes in blood volume and cardiac output, and compression of blood vessels by the enlarging uterus.
Hormonal Factors
- Pregnancy is characterized by high and stable estrogen levels throughout, but even subtle fluctuations in these hormone levels can trigger migraines in susceptible women 1
- While 60-70% of women experience improvement in migraine symptoms during pregnancy (especially in the second and third trimesters), some women (4-8%) experience worsening migraines, with a higher proportion of these being migraine with aura 2
- In rare cases (1.3-16.5%), migraine may appear for the first time during pregnancy, often with aura symptoms 2
Physiological Changes
- The enlarging uterus in the third trimester can compress the aorta and inferior vena cava, affecting blood flow and potentially triggering migraines 3
- Pregnancy causes a 30-50% increase in cardiac output, which peaks during the third trimester and can affect cerebral blood flow 3
- Systemic blood pressure gradually increases in the third trimester, returning to non-pregnant values by term, which may contribute to migraine attacks 3
Vascular and Respiratory Changes
- Pregnancy induces hypercoagulability with increased concentration of coagulation factors and fibrinogen, which may affect cerebral blood flow 3
- Functional residual capacity decreases by 10-25% during pregnancy as the uterus enlarges and elevates the diaphragm, potentially affecting oxygenation 3
- Oxygen consumption increases by 20-33% above baseline by the third trimester due to fetal and maternal metabolic demands 3
Other Contributing Factors
- Constipation, which occurs in 20-40% of pregnant women, is more common during the third trimester due to compression of the rectum by the gravid uterus and can trigger headaches 3
- Sleep disturbances, which are common in late pregnancy due to physical discomfort, can trigger migraines 4
- Stress and anxiety related to the approaching delivery can serve as migraine triggers 4
Management Considerations
- Non-pharmacological approaches should be the first line of treatment for migraines during pregnancy 4
- Paracetamol (acetaminophen) is the first-line medication for acute treatment of migraine during pregnancy 4
- Preventive medications should be avoided when possible, but if necessary, propranolol has the best safety profile during pregnancy 4
- Topiramate, candesartan, and sodium valproate are contraindicated during pregnancy due to potential fetal harm 4, 3
Monitoring and Follow-up
- Regular monitoring is essential when medications are used during pregnancy, especially for preventive treatments 4
- Active follow-up is necessary to determine treatment outcomes and provides the opportunity to review both diagnosis and treatment strategies 3
- Evaluation of treatment responses should include a review of effectiveness, adverse events, and adherence 3
Remember that migraine does not increase the risk for complications of pregnancy for the mother or the fetus, as the incidences of toxemia, miscarriages, abnormal labor, congenital anomalies, and stillbirths are comparable to those of the general population 2.