The woman who was crushed to death by a subway train at Union Square on Saturday lost her balance after fumbling with her iPad, causing her to fall onto the tracks, officials said.

Aracelis Ayuso, 21, was waiting for a Brooklyn-bound No. 4 train when she lost her grip on the tablet around 3:30 p.m., cops said.

When the East Harlem resident tried to catch the device, she apparently lost her footing, causing her to tumble forward and land on the tracks just as the train was coming.

The conductor spotted Ayuso’s body on the rails and tried to stop the train as it was pulling into the station, but it was too late.

Police originally thought Ayuso might have been drunk when she fell but said Sunday there were no obvious signs that she had been drinking. A toxicology report is pending.