Exploitative faith healers, whose practices are rooted in mystic Sufi lore, are common across Pakistan despite the disapproval of some schools of Islam.
In South Asia, a son is often believed to offer better financial security to parents than daughters.
The woman arrived at a hospital in the northwestern city of Peshawar after trying to extract the nail herself with pliers, doctor Haider Khan told AFP.
"She was fully conscious, but was in immense pain," said Khan, who removed the spike.
The mother of three daughters said she was pregnant with another girl, the doctor added.
An X-ray showed the five-centimetre (two-inch) nail had pierced the top of the woman's forehead but missed her brain.
Khan said a hammer or other heavy object was used to knock it in.
The woman initially told hospital staff she had hammered the nail into her head herself on the advice of the faith healer, before later saying he had carried out the act.
Peshawar police are trying to track down the woman in order to question him.
"We have collected the CCTV footage from the hospital and hope to reach the woman soon," city police chief Abbas Ahsan told AFP.
"We will soon lay our hands on the sorcerer," he said.
