Hi!! In some women, early menstrual cycle is a side effect to anesthesia. I had a laminectomy with spinal fusion in 2015 and immediately after surgery my period came very early. Never knew why. In February of this year I had the gastric sleeve and immediately when I "came to" my period also "came to"...two weeks early. Couldn't figure out why. I started doing research in the hospital and that is what I came up with.