On 12th April, 1671, Peter Rahm, a clergyman, gave an account of an event that took place, he averred, in 1660. One night he and Mrs Rahm were at home when there came a knocking on the door.
Rahm answered it to find without a small man, dark of visage. Rahm knew that this was a troll. The man said his wife was in labor and asked that Mrs Rahm could help deliver the baby. Obviously, trolls were not dabhands when it came to midwifery. Rahm prayed, then allowed his wife to go. He did not accompany them.
The wife described to him the way that they traveled. They seemed to be carried along by the wind. She delivered the baby. She was offered some food, but refused it. There seems to be a widespread idea that if you partake of food in the Realm or Dimension of Faerie, you will have to remain there. She was whisked home in the same way as she had arrived. The next morning she found a reward of silver on her shelf.
The text of Peter Rahm's declaration is to be found in Keightley's Fairy Mythology and in Grimm's Teutonic Mythology.
The tale of a human's being carried away to deliver the baby of an otherworldly being is quite common. This statement seems to indicate that it was not unknown for it to really happen sometimes. Perhaps occasional episodes such as this led to its becoming a widespread motif in folklore. It has been suggested that the women needing to be delivered are in fact human females that have been abducted by the otherworldly beings.
Of course, the rationalist will declare trolls don't exist - but the rationalist can be mistaken regarding the place where he draws the line between the possible and the impossible.