In order to determine the variability inherent in conceptus-related measurements in first trimester bovine pregnancies, conceptus and fetometric parameters from beef cattle pregnancies (n=103) estimated to be between Days 36 and 103 of gestation were examined. During this period, the protein concentration of amniotic fluid ranged between 0.181 and 0.501mg/mL. The amniotic fluid volume gradually increased from <1mL at Day 36 to 950mL at Day 103 (R(2)=0.9275) and amniotic compartment dimensions (length, R(2)=0.9713; width, R(2)=0.9802) increased predictably with fetal growth. Conversely, allantoic fluid protein concentration and volume correlated weakly with fetal age. A significant linear correlation existed between fetal crown rump length (CRL) and crown nose length (R(2)=0.9899) confirming that either measurement can be employed in the ultrasonographic estimation of fetal age. The amniotic compartment and fetometric data presented here have both research and clinical value, particularly in relation to fetal development evaluation and pregnancy viability diagnosis.