Is low blood pressure one of the early pregnancy signs?as well as dizziness?what causes these?

Yes.: Until the 18th to 20th week of pregnancy, elevated Progesterone levels (a hormone associated with pregnancy) relax blood vessel walls, resulting in a reduced blood pressure. This is commonly associated with lightheadedness upon standing. By the 18th to 20th week of pregnancy, this effect is countered by the increased blood pressure associated with the additional blood volume of the pregnancy.

Low BP: Low blood pressure is not a sign of pregnancy. Dizziness is not a sign of pregnancy either. It is seen frequently in pregnant women due to different factors such as fatigue, possibly dehydration in those who throw up a lot, etc, but per se they are not. What causes them? I cannot tell without more history and physical done.