Are There Pregnancy Chances After Missing Periods?

My wife is 30 year old and married for 3 years and trying for children. She has irregular periods from past few months and for that we consulted doc, taking medication. Her LMP was Sep-21 and doctor suggested her to take susten100 for 15 days from 18th day from her months start date.Now it is 40th day but still she did not get periods. Is there any chance of pregnancy. Please looking for your answer. Thanks.