BSM would lead to a (in my state, anyway) CPM (Certified Professional Midwife) license and more specifically, home birth and birthing center birth. MSN would lead to CNM (Certified Nurse Midwife) which usually practice in hospitals, and in groups with OB/GYNs, but may also practice in birthing centers or do home births. Many (not all) CNMs have a love for the midwifery model of care, yet do medical type interventions as well, for variety of reasons.
A nursing degree won't hurt you, in either case, but I'd really, really take the time to talk to a variety of midwives and see where your heart is, because Midwifery isn't medicine, and it's not nursing, either...but it can touch both at times.
Blessings to you!