'Heterogenous uterus' is a description used to describe the appearance of the uterus after an ultrasound exam is done. All that this means is that the ultrasound appearance of the uterus is not totally uniform. The two most common causes of heterogenous uterus are uterine fibroids, which are benign muscular growths in the uterine wall, and adenomyosis, which is a proliferation of the normal uterine glands into the muscular wall of the uterus. These conditions are very common, affecting up to maybe 50% of women by middle age. They generally cause no symptoms but they can cause abdominal pain
and heavy bleeding
and cramping with menstruation. Mild to moderate cases of either fibroids or adenomyosis probably do not have any pronounced effect on the ability of a women to have a baby. As always the diagnosis and the management of your girlfriend's particular condition is best done by the doctor
who is following her condition already. Setting up an office visit to discuss an concerns with her OB / GYN doctor is advised.