Y37 fetus ultrasound. Reproductive ultrasound image of dolphin Y37 showing an approximately 18-week gestational age fetus in a longitudinal plane, acquired in August of 2011. Dotted line shows the skull biparietal diameter, which is used to estimate gestational age and parturition date. Boat-based surveys documented that the pregnancy was successful. Dolphin Y37 was seen with a live calf in both April and August of 2012.