Pregnant mare serum gonadotrophin (PMSG) is detectable in mares between days 40-120 of gestation when functional endometrial cups are present. Peak concentrations in most mares occur between days 60-80. Variation in levels between mares means that a negative test result before 60 days or after 90 days from breeding does not rule out pregnancy. The test is a latex agglutination test, with results reported as positive or negative. A positive result generally indicates pregnancy but false positives do occur if there has been foetal death after the endometrial cups have formed (i.e. after day 40).
Progesterone can be used for pregnancy diagnosis between days 12-22. Oestrone sulphate can be used from days 100-310.