'In labour your bones move backwards.' The magical childbirth photo women are sharing.

Warning: This post contains a graphic photo of a woman in labour.

An incredible photo of a woman in labour has been shared around the world, surprising even women who have given birth.

Tangi Birth Services (TBS) in the US posted the photo earlier this month. It shows a woman leaning over a hospital bed, with a large bulge protruding from her lower back.

“Can you see that bulge on her lower back? That is the rhombus of Michaelis,” TBS explained in the caption.

“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 opening of the back.

“This is completely normal and is in fact an integral part of a physiological birth as it allows your baby the maximum amount of space to turn as they navigate their way out into the world.”

TBS added this was the reason they encouraged mums to deliver in “upright and leaning forward” positions.

“Your body was made to do this! And your body and your baby work together!” the post continued.

“Birth is not something to be feared… it is something to be understood!”

TBS also explained they were sharing their knowledge because, “this post is about showing how important it is to deliver how your body wants and not just on your back in a bed like many OBs will “make” you do.”

The image was originally shared by North Dallas Doulas on Instagram, where Dr Sarah Wickham explained the background of the photo.

“This second time mum had a precipitous/rapid birth, and used chiropractic care throughout her pregnancy and postpartum,” she wrote.

According to Dr Wickham’s website, the rhombus only protrudes for “a matter of minutes”, before it retracts after serving its purpose.

The post of the photo on the TBS Facebook page this month went viral, being shared more than 50,000 times. Hilary Rorison, an Australian midwife and midwifery advisor with The Australian College of Midwives, saw the photo, too.

“It’s amazing this image is getting so much attention,” she told Mamamia.

“The more women are aware of the ways they can work with their bodies during labour, the better.”

Rorison explained that a woman’s ligaments loosen during pregnancy, to prepare the body for delivery. This is primarily due to the hormone relaxin.

“A non-pregnant pelvis is rigid, but one about to deliver needs to be loose,” she explained.

“It is the mum’s mechanism for adjusting for the baby. And it’s one of the reasons why we now suggest women get off their backs during labour, because lying on your back stops the body from making the last adjustments.”

Women who delivered through a caesarean section, however, may not experience what the woman in the photo did, because that usually only happens in a later stage of labour, as the head is lower.

“The bulge normally happens at the pushing stage,” Rorison explained.

“Some women do have movement of their coccyx bone, too, but that is very rare.”

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The comments section on the TBS Facebook page was filled with mothers amazed this bone movement had been happening to their bodies.

“This makes so much sense why my back pain has been so excruciating during both my labours,” said one mother. “I was on my back to deliver both. This third baby I’m going to get off my back and hopefully I’m in less pain.”

Another wrote, “Wow. Just wow. I gave birth four times and never knew this.”

A nurse even added, “I have NEVER heard of this and I’m a nurse!”

There were also many comments of frustration from mothers who felt they had been forced to deliver on their backs, and weren’t allowed to be forward-facing. One mum said, “They never mentioned nor offered this position. I was kept on my back only.”

The choice about birth positions has become an increasingly loud discussion in recent times, as more mothers want to choose what feels natural, and comfortable, to them at the time.

For example, earlier this year, a mother shared her concerns about giving birth whilst lying down, asking, “Am I being unreasonable to refuse to lie down during labour?”

Dr Philippa Costley, a Melbourne obstetrician/gynaecologist and spokesperson for RANZCOG (the Royal Australian and New Zealand College of Obstetricians and Gynaecologists), told Mamamia that, “A woman has the right to choose to birth in any position she wants, as long as there’s no urgent situation requiring immediate delivery.”

“For example, if an urgent instrumental delivery was required if the baby was showing signs of severe distress.

“Women should discuss their preferences and options with their care provider, both before and during labour.”

In Dr Costley’s experience, childbirth whilst being on one’s back is the most common position, but it isn’t what always happens.

“For some women, they find it more efficient with pushing if they’re sitting on the bed,” Dr Costley said. “The rate of perineal trauma can be reduced in that position.”

“However, some women do prefer to birth on all fours or their side, and that’s fine.

“I have patients who birth crouching, but it’s something to be monitored as sometimes you can have poor control in that position. As the baby’s head is being delivered, the speed and safety can be difficult to control.”