Pregnancy in owl monkeys was monitored using ultrasonography. The obstetric exams were performed using a 5-12 MHz linear probe. The measurements included the mean gestational sac diameter (MGSD), crown-rump length (CRL), biparietal diameter (BPD), occipitofrontal diameter (OFD), head circumference (HC), head area (HA), abdominal circumference (AC), abdominal area (AA) and femur length (FL). The Pearson’s correlation coefficient showed highly significant positive correlations between most of the fetal growth variables (r > 0.90, P < 0.01). The AC x FL and AA x FL correlations did have correlation coefficients <0.90, although this value was still highly significant (P < 0.01). These results suggest that all of the fetal growth variables are strongly associated with each other