Can losing lower abdominal fat lead to menstrual irregularities?

Indirectly. Depends.: The loss of lower abdominal fat alone does not have a direct causal relation to loss of menstrual cycles. However, depending on how you went about losing the fat, you could have contributed to the loss or disruption of your menstrual cycles. Extreme exercising, fasting, anorexia, can lead to irregular menstrual cycles. Without more info too many possibilities. U should see your gyn to discuss.