When do stretch marks occur?

Depends: Some women do not get stretch marks. It seems to be determined by genetic predisposition. Generally they start to develop after about 7 months.

Third trimester: Generally, stretch marks will occur after a pregnant mom begins to really show. They occur more commonly later in pregnancy.

Stretch marks: Stretch marks are scarring of the dermis. They occur when there has been rapid growth and stretching of tissue like in growth spurts, pregnancy and obesity. They fade over time.