In Celebration of the OP Baby

intervention physiology

How many times have you heard "I had to have an epidural/c-section/ventouse/etc. because my baby was facing the wrong way"? An occipito posterior (OP) position occurs when the baby enters the pelvis facing forward with their back towards their mother's back. The back of the baby's head (the occiput) is in the back of the pelvis (posterior) against the sacrum. Between 15-30% of babies start labour in an OP position, but less than 5% will remain in this position at birth. An OP position is associated with medical intervention during labour: syntocinon infusion; epidural; forceps; ventouse; c-section. This post will discuss whether an OP position is actually a problem, or if the problem lies in our beliefs about, and 'management' of this normal variation.

Occipito posterior physiology

You don't need degree-level knowledge about pelvic anatomy to understand how the pelvis functions during labour. The pelvis is shaped in a way that requires the baby to rotate during labour. If you look in textbooks you will find diagrams with exact measurements of various pelvic diameters and categorisations of pelvic types. This is nonsense because every woman's pelvis is individual and they don't come in 'types' [1]. The pelvis is also not a fixed structure. The bones of the pelvis are held together by ligaments that allow it to open up to create more space during labour.

I find it more helpful to consider that there are 3 areas of the pelvis: the brim, the cavity and the outlet.

The baby usually enters the brim with their head mostly facing sideways ie. transverse or oblique (to fit the shape). It doesn't really matter where the occiput is when the baby enters the pelvic brim because once in the cavity the baby can rotate. The downward pressure of the contractions and the tension and shape of the pelvic muscles will guide them into a direct occipito anterior (OA) position and through the outlet. However, a very small number of babies will rotate to a direct OP position and come out facing the front of the pelvis.

Watch this movie for an overview of the normal physiology of OP labour:

Of course, OP and OA babies may use this turning space to do all kinds of interesting things from turning OA to OP, to rotating all the way around the back of the pelvis to end up OA. The baby will work out the best way to move through their mother's pelvis, even if we don't understand it. Some babies are born in the OP position either because they stay in that position, or because they rotate into that position during labour (from OA). You can watch the birth of a big OP baby in 'The Birth of Beau'.

Creating a problem

An OP position in labour was not considered a problem until routine vaginal examinations began to be used to assess labour progress. Even then, obstetricians were not concerned about an OP position unless a problem occurred. Friedman (1950s -70s), famous for his research that plotted women's cervixes onto graphs, found no difference in the length of labour when a baby was in an OP position.

However, in more recent years an OP position has been blamed for all manner of problems and complications. These unsubstantiated accusations reflect modern misunderstandings and mismanagement of a physiological variation. Let's take a look at some beliefs about an OP position and bust some myths.

Postdates pregnancy?

There is no evidence that an OP position causes a pregnancy to go past the guess date.

Pre-labour rupture of membranes?

No evidence.

Back pain?

Some women will experience pain differently when their baby is in an OP position. However, it is difficult to determine if this experience of pain is due to the position of the baby, or other factors. One study [2] exploring back pain in labour concluded that the assumed relationship between fetal position and back pain in labour is a dominant discourse, albeit one which is lacking in empirical credibility. Plenty of women with an OA baby complain of backache in labour, whilst many with an OP baby do not. Unfortunately, women are told that OP labour is 'worse'. Given the psychological and emotional aspects of pain perception, this is not helpful. Every birth experience is also different. I cared for a mother during two births. Her first baby was in an OP position and she had a four-day stop-start contraction pattern before labour established. Apart from being tired, she coped well with the pain throughout. Her second baby was OA and labour established quickly. She was shocked and distressed by how much more pain she experienced with her OA baby compared to her previous OP baby.

Women with an OP baby are more likely to opt for (or be persuaded to have) an epidural. This is not surprising, considering they are led to believe their labour will be more painful and prolonged. They are also more likely to be subjected to interventions that increase pain and risk. For, example, a woman with an OP baby is more likely to be told her labour is slow and have augmentation (see below). Both medical methods of augmentation—ARM and/or syntocinon (pitocin) increase pain. Once an epidural is inserted, the ability of the baby to rotate into an OA position is reduced [3]. The woman is unable to instinctively move her body and work with her baby to facilitate rotation. In addition, the pelvic 'floor' (more like a bowl shape) is anaesthetised and loses tone, taking away the resistance that assists rotation.

Prolonged labour?

Labour patterns are often different with an OP baby. This is a physiological variation and is perfectly normal. It is difficult enough for a woman with a baby in an OA position to fit prescribed patterns of labour progress and even more difficult with an OP position. There are two common differences in labour pattern when a baby is OP:

Contraction pattern

Early labour (the separation phase) can take longer to build with more stops and starts. Once in strong labour, the woman's contraction pattern is likely to be irregular. This irregular contraction pattern may the baby more opportunity to rotate between contractions ie. while the uterus is relaxed.

Cervical dilation pattern

Women with an OP baby are more likely to be incorrectly diagnosed with 'failure to progress' if their cervical dilation is being plotted onto a graph. To understand why, you first need to understand how the cervix opens in labour. Below is an overview featuring an OA baby:

The key difference with an OP baby is that the cervix is not held open until the baby enters the pelvic cavity and rotates (or not). The common pattern is that the cervix appears to be not doing much while the fundus is busy forming. Then, once the baby descends and rotates, the soft and stretchy cervix gets quickly pulled over the baby's head. The birth is often very quick once this happens (if physiology has been supported rather than disrupted with interventions to 'speed up' the opening of the cervix).

'Premature' pushing?

An 'early' urge to push is also a normal aspect of OP labour. As the OP baby descends through the pelvis the occiput puts pressure on nerves in the back of the pelvis creating an urge to push. This pushing helps the baby to rotate by increasing downward pressure onto the cervix and pelvic muscles because the baby can pivot against this tension. An anterior cervical lip is a normal part of all labours, but is more likely to be found if a vaginal examination is carried out in response to spontaneous pushing to 'check progress'.

Deep transverse arrest?

A deep transverse arrest (DTA) is a rare complication incorrectly blamed on an OP position. There is no evidence to support this idea and obstetricians were trying to bust this myth as far back as the 1950s [4]. Today most DTAs are not actually DTAs. Instead, they are a failure to wait for the baby to rotate due to non-evidence-based timeframes. Most babies will be in a transverse position at some point in labour during their rotation through the pelvis. Unfortunately, when c-sections are done due to failure to wait, women are often told they had DTA. However, real DTA involves no rotation and no descent and a truly obstructed labour. This is rare.

Selling a solution

Anyone who knows about marketing knows that first, you must identify a problem, and then sell the solution. An OP position has (wrongly) been identified as a problem for labour progress and outcomes. The solution being sold reflects the culture in which obstetrics developed – a perception that women's bodies are inefficient and malfunctioning and can be improved on by interventions enacted by experts. However, today it is not just obstetrics reflecting and transmitting this disempowering message to women. It is also a common approach within the 'alternative' or 'natural' childbirth culture. The solutions being sold centre on changing the woman's body/baby rather than changing the dominant discourse about labour progress.

Fixing women's non-conforming bodies

Medical approach

Medical solutions to 'failure to progress' include trying to speed the labour up by first breaking the waters if they are still intact. This reduces the amount of fluid around the baby, reducing their ability to rotate and doesn't speed up labour. The next step is to augment the labour with syntocinon (pitocin) which increases pain (and use of epidural) and the chance of fetal distress. However, if the mother and baby manage to cope with induced contractions, syntocinon will speed up labour. Another medical intervention gaining popularity is manual rotation of the baby's head by putting a hand into the woman's vagina, gripping the baby's head and rotating it from OP to OA. There is insufficient evidence to support this invasive intervention [5].

Non-medical approach

Solutions offered in non-medical 'alternative' approaches can start in pregnancy. Blame for an OP position is placed on the woman/baby. Women are given advice about 'optimal fetal positioning' implying that they have control over the position their baby is in when there is no research evidence to support this notion. A 2024 Cochrane review [6] attempted to assess whether maternal positions in late pregnancy improved outcomes. The reviewers only found two old studies (1983 and 2004) and neither was of good enough quality to be included in a systematic review. An earlier Cochrane review [7] looking at hands and knees posture in late pregnancy or labour for fetal malposition concluded that the use of hands and knees position for 10 minutes twice daily to correct occipito‐posterior position of the fetus in late pregnancy cannot be recommended as an intervention.

Women are also told that the shape of their pelvis is not optimal due to its structure (type/category) and/or tension in ligaments or tissues. Commonly, women are told their pelvis is 'misaligned' requiring interventions to balance. These interventions involve someone with 'expertise' manipulating the woman's body into particular positions. Or in some cases performing internal techniques during a vaginal examination. The latter has echoes of medical history when physicians performed vaginal examinations early in pregnancy to assess the 'adequacy' of the pelvis.

Once women are in labour non-medical interventions are used to get the woman's body to fit institutional non-evidence-based parameters of progress. Midwives, doulas and birth workers often intervene in an attempt to save the woman from unnecessary interventions. They give instructions about movement and positions and use hands-on techniques aimed at getting the baby to rotate quicker. There are no studies demonstrating these interventions are effective for women having a physiological birth ie. without an epidural [8, 9,10].

Regardless of the type of intervention — medical or alternative — the underlying beliefs/principles are the same:

OP is a malposition that requires intervention (the woman's body is wrong).
Women's bodies need intervention to fit medical timeframes (rather than disregarding those timeframes).
External expert knowledge and skills are more powerful than women's body-wisdom, instincts and intuitive movement.

Suggestions

OP in late pregnancy

Pregnancy is a time to build and nurture self-trust and reinforce the woman as the expert. It is not a time to disempower her and reinforce fear and external expertise. Care providers should:

Reinforce the woman's trust in her body and baby, and her innate wisdom and intuition (that includes knowing if she needs help).
Discuss the possibility that her labour may be different (not better or worse) and might not fit general expectations about labour patterns/progress.
Remind her that the baby will turn once they get into the pelvic cavity in labour, or may even be born OP.
Tell her positive OP birth stories and connect her with other women who have experienced positive OP labours.

Spontaneous, physiological OP Labour

Trust the mother and her baby to birth.
Provide an environment where she can instinctively move and work with her baby to facilitate rotation (without instructions).
Don't do vaginal examinations. They are ineffective at determining labour progress with an OA baby, never mind an OP one.
Don't tell her not to push if she is spontaneously pushing—regardless of cervical dilatation (again, don't do a VE).
Back pain can be relieved by a forward-leaning position [7, 11]; warm water; gentle sacral pressure or sterile water injections [12]. Avoid applying strong pressure to the sacrum as this may reduce the space available in the pelvis for rotation.

Summary

An OP position is not 'wrong' or a problem. It is not caused by anything the woman does or does not do. Instead, it is a common variation that occurs when a baby gets into the 'optimal position' for their journey through their mother's unique body. After all, the baby has more knowledge about the interior of their mother's pelvis than we do. If we want to improve the experience and outcomes associated with an OP position we need to rethink our approach to it. Let's celebrate the OP baby and women's body-wisdom and support birth to unfold as it needs to, only intervening if it is truly required.