Mila Kunis prefers to be naked.

A source told US OK! magazine: "She's so big, and the baby is moving a lot.

"Nothing makes her feel more comfortable and relaxed than being naked."

Mila - who is having her first child with fellow actor Ashton Kutcher

- is expected to give birth in the next couple of months.

The source continued that Ashton "doesn't mind in the least" but fears his fiancee will want to "come up with fun activities to get out of the house".

Meanwhile, another source has revealed that Mila is keen to have a natural birth but doctors have advised her otherwise.

The source explained: "Mila was going to do an all-natural birth with no medications or sedatives, but she has been advised against this because she is such a small girl.

"Ashton will not accept this and refuses to see her in pain."

The couple are reportedly due to marry next summer in a low-key ceremony.