Most patients begin to notice some lightheadedness in the last part of pregnancy: especially when they may stand up from a sitting or lying down position. Due to the effects of progesterone from the placenta, a pregnant woman’s blood pressure will drop during pregnancy (during the 2nd trimester with a slow rise in the 3rd trimester). Drinking plenty of fluids can help alleviate some (but not all) of these symptoms.
If dizziness occurs just before meal times, then hypoglycemia is the usual cause. The placenta siphons off the blood sugar out of a pregnant woman’s blood stream in order to transport it over to the baby. The best way to avoid these symptoms is to have a healthy snack in-between meal snacks.
Fainting is a classic symptom of pregnancy: many older motion pictures portrayed young women fainting or swooning to the ground. At that point the other characters would classically blurt out, “She must be pregnant!” Fainting is caused by a loss of your blood pressure when standing still (or standing up) for a period of time. A significant portion of your blood volumes “pools” into the distended deep veins in your legs (caused by the combined effects of gravity keeping the blood volume down in the relaxed dilated walls of the veins). It is recommended “to keep moving” especially when standing, sitting when traveling by car or plane, or quickly getting up from a horizontal position. Keep flexing your leg muscles and, when getting up, hold on to some support so that if you feel faint you can brace your possible fall.