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:

1. You ovulate less often, so your chances of getting pregnant over time are less (for example, if you ovulate on CD 14, then you ovulate on average 13 times per year, but with a 39-day cycle you ovulate on CD 25, or only about 9 time per year, which is about one-third fewer times).
2. Delayed ovulation may be a sign of poor egg quality.
3. Even if fertilization occurs, with delayed ovulation the endomtrium (uterine lining) has aged since the beginning of your cycle and may no longer be ready for the implantation of the fertilized egg.