An incredible photo of a woman's bones moving during child birth has gone viral, with the post praised for its "amazing" message about the power of the female body.
US pregnancy care centre Tangi Birth Services shared a photo of a woman giving birth on its Facebook page earlier this month.
The photo shows a woman squatting over a hospital bed as medical staff attend to her, with a bulge visible in her lower back, news.com.au reported.
"Can you see that bulge on her lower back? That is the rhombus of Michaelis," the caption explained.
"During the second stage of labour, a combination of bones including your sacrum actually move backwards and in doing so, increases the diameter of your pelvis."
Known as the "opening of the back", the Facebook post stressed that the movement was "completely normal".
"It allows your baby the maximum amount of space to turn as they navigate their way out into the world," the post read.
"In order to facilitate the opening of your back, you should use active birth positions where you are upright and leaning forwards … Your body was made to do this! And your body and your baby work together!
Birth is not something to be feared … it is something to be understood!"
The photo was originally shared on North Dallas Doula Associates' Instagram page earlier this year.
North Dallas Doula Associates director Melissa Espey-Mueller took the original photo and told Mom.com she was "thrilled" to have been able to take a photograph showing the opening of the back.
"I have been a doula for 20 years and have been eager to find a photo showing this physiologic occurrence for some time," she said.
Tangi Birth Services' post has since gone on to receive more than 22,000 comments and 50,000 shares, with many women admitting they had never heard of this happening.
"Wow. Just wow. I gave birth four times and never knew this," one commented.
"My husband told me about this! I give birth on my knees and he said the base of my back pushed out … And ouch! No wonder I found labour worse on my back! I soon flipped over," another mum wrote.