Early Pregnancy Diagnosis by Weight Measurement in the Sprague Dawley Rats: A New Method

An early diagnosis of pregnancy in Sprague Dawley (SD) rats is of great importance for scientific research in reproductive health and perinatology. However, the commonly used methods, vaginal embolus check and vaginal smear for sperms, are not always satisfactory in practical courses. To explore a more convenient method for practice in identifying the pregnant SD rats at an early stage, we hypothesized that differences among weight changes may separate pregnant SD rats from the unpregnant effectively.

The initial weight (W₀) of SD female rats before mating and the weight of them from day 6 to day 12 after mating were recorded, then gained weight (ΔW) was calculated. Pregnancy was confirmed when female rats gave birth on day 23 or earlier.

In total, weight changes data of 34 pregnant rats and 49 unpregnant rats were collected. Weight gains of pregnant SD rats on the 6^th day were found different from those in unpregnant SD rats significantly and a diagnostic model of ΔW on gestation day 6 (ΔW₆) has been set up to distinguish pregnant SD rats with 70.00% sensitivity and 100.00% specificity. Diagnostic data models of ΔW₇ ~ ΔW₁₂ owned higher sensitivity and specificity respectively. Cut-off values of ΔW₆ ~ ΔW₁₂ were correspondingly 25.50 g, 23.00 g, 22.50 g, 22.50 g, 31.00 g, 27.00 g and 31.00 g. Practically, diagnostic models of weight gains showed robust potential in affirming the pregnant SD rats at early stage of gestation.