Cocaine during pregnancy?

My wife is 4 months pregnant, and I used cocaine with friends this weekend for the first time in years. Could my semen be tainted and affect the baby at all at this stage, either oraly or ly? Should I avoid completely, and for how long? My wife has no idea I did this with the guys, so what can I say to her? I know it was stupid, but it was a mix of old college friends and alcohol, whats done is done.