How likely is it to get pregnant with irregular periods?

Harder, but possible: Irregular periods indicate sporadic (if at all) ovulation, so it is much much harder to conceive (if possible at all) with irregular menses. If you are 48 years old, then your chances of conceiving spontaneously are very low also due to the likelihood of having diminished ovarian reserve, and 'poor' quality eggs to be ovulated. Age related decline.