Liz: You wondered how long it would take to become severe. Just had time to quickly pull 2 charts. Baby #1 : BW 6#0oz. Full term. Admitted as a 10 day old, weight 4lbs. 4oz. Mother pumped with Medela 015, double kit. First 4 pumpings after admission ranged from 5-15cc. Baby's sodium was 169, on ventilator in ICU. Baby #2: BW 8#4oz. Full term. Admitted as a 8 day old, weight 6#8oz. Did not require admission to the ICU. This mom's supply was OK. Pumped 11oz in first 10 hours after baby's admission. Baby had a high palate, receding chin, tongue tie. After clipping could still not obtain adequate volume at breast. With SNS did hear 1 suck per swallow, volume from SNS OK. Mother however choose to pump and bottle feed, which the baby did without any problems. Hope that gives you some idea. Laura Wham, RN,IBCLC