This can vary from woman to woman, but a woman's cycles will generally regulate by the 6th full cycle after fertility returns. There may also be a relationship between regularity and the timing of when the first period occurs. Women who start having periods earlier on in their breastfeeding may have longer-lasting irregularity and those who resume their periods further into their journey may return to a normal cycle more quickly. And some women may not have a regular period until after their baby is fully weaned.