Why it happens
Rising hormone levels during pregnancy cause your blood vessels to relax and widen, increasing blood flow to your baby but lowering your blood pressure. This can reduce blood flow to your brain, temporarily causing dizziness. Most common after your first trimester, feeling lightheaded, dizzy or faint can also result from becoming overheated, having low blood sugar or getting up too quickly from a reclining or sitting position.
What to do
When resting, lie on your side (the left side is best) to help prevent low blood pressure caused by the uterus compressing your vena cava and aorta. When getting up, be sure to rise slowly. Dizziness can also be a sign of dehydration, so drink plenty of water. Try to eat smaller meals throughout the day and carry a snack with you, such as fruit or crackers, for a quick blood sugar boost. If you feel faint, sit with your head between your knees or lie down with your feet higher than your head. If you do faint, contact your doctor immediately, as this may be a sign of severe anemia.