How do i know if my mare is in foal? (unfortunately can't afford vet)?

if you can't afford the vet you can't afford the foal (who will be very expensive), the stud I work on have worked out that once the foal is born it costs them well over �1500 in the first year. It will be kindest to the horse & potential foal to either sell her or loan her to someone who can afford to deal with a foal.