[Development of a cytological method to detect pregnancy in guinea pigs]

Diagnosis of guinea pig pregnancy by the inhibition hemagglutination test used to detect chorionic gonadotrophin in urine showed to be unreliable after the 57% false positive and 3% false negative results obtained over 79 urine samples tested. On the other hand, by comparing the cell morphology of about 60 vaginal smears taken from 20 non-pregnant guinea pigs, stained by a Papanicolaou modified technique, the 4 estrous cycle stages were characterized. The subsequent study of many vaginal smears taken from 15 pregnant guinea pigs showed no pathognomic cells but a picture where 60-70% proestrus and 40-30% diestrus cells appeared. This proestrus-diestrus (Pd) picture was accepted as typical for pregnancy, because it showed up in every pregnant guinea pig lasting all the gestation period, changing only after delivery or abortion. Fecundation does not change the estrous cycle sequence which, as it was proved, progressed normally until it reached this Pd picture. Therefore, the persistence of a Pd picture during +/- 6 days should be considered as diagnosis for pregnancy; when estrus has been detected a Pd picture 12-14 days post estrus as prognosis, and at 16-19 days post-estrus as diagnosis for pregnancy. This cytologic assay proved to be reliable. Besides, once cell characterization has been performed, the staining procedure can be substituted by a direct observation of wet specimen, saving time without loosing accuracy.