A menstrual cycle with infrequent menstrual periods and cycles that are consistently longer than 35 days is also known as 'oligomenorrhea.' Oligomenorrhea usually reflects irregularity of hormonal events coming from the ovaries. You first should determine when during your cycle ovulation happens. In a 39-day cycle you would expect it to happen around CD 25, and because it happens after CD 21 it's considered delayed ovulation.
The first thing to do is to start a fertility and temperature chart. This will confirm exactly if and when you ovulate.
Delayed ovulation may possibly decrease your chance of conception for several reasons: