Massof, who pleaded guilty to two counts of third-degree murder, said he witnessed about 100 babies born alive before having their spinal cord "snipped" to ensure death, the AP reported at the time.
White House spokesman Jay Carney commented on the case Monday.
"The president does not and cannot take a position on an ongoing trial, so I won't as well," said Carney, USA Today reported. Carney said Obama was "aware" of the trial and added, "certainly, the things that you hear and read about this case are unsettling."
Gosnell faces the death penalty if convicted. Several former employees, including his wife, have pleaded guilty to various charges.