There is no harm in taking aspirin
before conceiving. But there is no proven benefit also. Starting aspirin may not solve your problem. You need some investigations to find out cause for repeated miscarriages. Though these investigations are costly, if abnormal some factors can be corrected to avoid miscarriage. You can ask your doctor about those investigations. Some basic cheap investigations are blood sugar level, VDRL
, USG (Transvaginal) to find out uterine problems. Costly investigations like karyotype
can be done or deferred according to your doctor's advice.
Wish you good health.