| OA/BVM | oral airway/bag-valve-mask |
|---|---|
| OAS | old age security; oral allergy syndrome; osmotically active substance |
| OAW | oral airways |
| OC | obstetrical conjugate; occlusocervical; office call; on call; only child; optic chiasma; oral contra... |
| OCA | oculocutaneous albinism; olivopontocerebellar atrophy; oral contraceptive agent |