hello, Some studies have shown low does of aspirin beneficial in preventing preeclampsia. Low dose baby aspirin is sometimes used in early pregnancy to prevent miscarriage where clotting or bleeding factors are suspected.May be this is the reason why your doctor prescribed you aspirin.But actually aspirin is avoided in pregnancy due to its blood thinning effect which may result in abbruption of placenta so please consult your doctor clearly and ask them if you have any doubts.Previous history of placenta previa may have chances of having this time also so follow the instructions given by your doctor.Thank you take care.