What Are The Chances Of Pregnancy When Having Irregular Periods?

Hi Dr .my wife's cycle period has stopped last 3 months .her weight is more than 100 kg .she is 42 years old.we have tree children.my last child age is 11 years old.we want to hv more children.first I want regularize her cycle period.hense can she use prigylotun tablets now?if yes how and when?
Kindly help me.