Warning: Graphic content.
An incredible photo of a woman in labour has gone viral, revealing the way in which a body's bone structure can shift during birth to make way for the baby.
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In the photo, shared by US centre Tangi Birth Services, the woman is bent over a hospital bed, with a clear bulge in the middle of her lower back.
"That is the rhombus of Michaelis," the photo's caption explains.
"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.
"This is what is known as the opening of the back."
The caption adds the shifting of the bones is "an integral part of physiological birth", as it allows the baby the maximum space to make their way out into the world.
The post has racked up over 40,000 likes and 50,000 shares, with many women taking the opportunity to share their own birth experiences
"I gave birth in my room all alone and this is exactly the position my body went in to deliver. Amazing. Our bodies are so powerful," one woman observed.
"My husband told me about this! I give birth on my knees and he said the base of my back pushed out. Fascinating to see a photo of it thank you," wrote another.
"And ouch! No wonder I found labour worse on my back! I soon flipped over."
According to a report from the International Journal of Obstetrics and Gynaecology, of women who are allocated the upright position during birth, 74 percent favour kneeling, leading to more intact perineums and a reduction of forceps deliveries.