For those of you who refuse to use the Blank Rune in your runesets, you will be pleased to know that you can use Pertho as your "blank rune." For that reason, please read the section on the Blank Rune to understand how Pertho will work for you in your readings.
For me, though, Pertho indicates a birth. When it is upright, the rune itself looks like an opening womb to me. That automatically leads to Pertho being indicative of the sexual aspect of relationships, especially if it appears paired with Gebo.
Pertho can also indicate those talents and potential that have been hidden up until now. It can also indicate that the querent has occult tendencies or an ability as a medium, and it is likely that the querent was not consciously aware of those abilities beforehand.
When reversed, Pertho can mean death, whether of the body or of a situation. In relationship questions, it often indicates sexual incompatibility or sexual dysfunction.
Pertho reversed can also indicate that the querent has been indulging in uninformed occultic dabbling.