Updated: February 2022
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 (Sizer & Nirmal 2000). 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 common variation.
A bit of anatomy and physiology
I’m assuming that readers of this blog are midwives, doulas, and/or birth nerds who have an understanding of the pelvis. If you don’t, it doesn’t really matter – knowing the names of the bones doesn’t help you understand how the pelvis works. Basically, 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 – this is nonsense as every woman’s pelvis is different and they don’t come in ‘types’ (Betti & Manica 2018; Kuliukas at al. 2015; Tennenhouse 2018).
I find it more helpful to consider that there are 3 areas of the pelvis: the brim, the cavity and the outlet. These areas have slightly different shapes, as I’ve tried to demonstrate below: The baby usually enters the brim with their head mostly facing sideways ie. transverse (to fit the shape). It doesn’t really matter which way the baby’s head is when entering the brim – once the head is 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 (see below).
Usually, the baby will take the shortest rotation into a direct OA position. So, a baby entering the pelvis in a ROA (back = front/right) does this:
Whereas a baby entering the pelvis in an ROP (back = back/right) position does this:
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 – even if we don’t understand it.
Being born OP
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‘.
OP labour patterns
Labour patterns are often different with an OP baby. This is a physiological variation and is perfectly normal. It is important to understand why and how physiology differs with this position. 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—particularly with a first baby.
Firstly, a baby who enters the brim in an OP position may not fit quite so snuggly on the cervix and this may increase the chance of variations such as ‘post-dates’ pregnancy and/or rupture of membranes before labour. 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.
These situations only become problematic when we apply generalised expectations about how labour should be to an individual woman/baby and situation. It becomes more of an issue if vaginal examinations are used to assess progress. With an OP labour, the fundus forms in the same way as with an OA labour. However, the cervix is not held open like it is with a well-flexed OA baby. Therefore, it appears not to be opening if you feel it – resulting in an incorrect diagnoses of ‘failure to progress.’ Instead this is a failure to understand the transformation of the uterus during labour.
Here is how the fundus/cervix function with an OA baby (once I find my lost apple-pencil I’ll create an OP version).
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 up. 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).
An ‘early’ urge to push is also a normal aspect of OP labour. As the OP baby descends through the pelvis the back of their head puts pressure on nerves creating an urge to push. This pushing may be the body’s way of helping the baby to rotate by increasing downward pressure onto the cervix and pelvic muscles – the baby can pivot against this tension. An anterior cervical lip is also common.
Trying to make labour patterns (women) conform
If cervical dilatation is being used to assess labour progress it is very likely that ‘failure to progress’ will be diagnosed. The medical response to this is to break the waters if they are still intact. This reduces the amount of fluid around the baby, reducing their ability to rotate. The next step is to augment the labour with syntocinon (pitocin) which increases pain (and use of epidural) and the chance of fetal distress.
The alternative approach is to use non-medical interventions to get the woman’s body to fit institutional non-evidence-based parameters of progress. Midwives, doulas and birth workers often intervene with techniques and direct women into various positions 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 (Desbriere et al. 2012).
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).
- That women’s bodies need to be intervened with to fit medical timeframes rather than disregarding those timeframes.
- External expert knowledge and skills are more powerful than women’s instincts and intuitive movement.
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. A study by Lee, Kildea & Stapleton (2015) into back pain in labour concluded: “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’, and are told horror stories like the one I started the post with. Given the psychological and emotional aspect of pain perception, this cannot be 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 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. 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. 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 (Lieberman et al. 2005). 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 its tone, taking away the resistance that assists rotation. In this situation (ie. non-physiological labour), positional interventions may help to rotate the baby (Bueno-Lopez et al. 2018).
In terms of back pain during labour (regardless of baby’s position), sterile water injections (into the skin of the lower back) are effective in providing relief (Fogarty et al. 2008; Lee et al. 2017).
Women can blame themselves for their baby being in an OP position. They question what they did (spent too long in the car) or didn’t do (scrub floors). Often the advice they are given antenatally about ‘optimal fetal positioning’ implies that they have control over the position their baby is in when there is no research evidence to support this notion. In fact, the little research that has been done demonstrates that hands and knees posturing in pregnancy makes no difference (Hunter, Hofmeyr & Kulier 2009; Kariminia et al. 2004). I have even heard of women being told that their baby has assumed an OP position because of their unresolved emotional issues!
Pregnancy is a time to build and nurture self-trust, to reinforce the woman as the expert. 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 to birth.
- Discuss the possibility that her labour may be different (not better or worse) and might not fit general expectations about labour patterns/progress.
- If she wants to, she can try a variety of techniques to encourage the baby to turn (even though the research suggests it will probably be ineffective). However, if the baby doesn’t respond, it’s because they have chosen their optimal position for labour. The baby knows the shape of their mother’s pelvis better than any care provider.
- Remind her that the baby will turn once he gets 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.
- Trust the mother and her baby to birth.
- Provide an environment where she can instinctively move and work with her baby to facilitate rotation.
- 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 (Stremler et al. 2005); warm water; gentle sacral pressure or sterile water injections. Avoid applying strong pressure to the sacrum as this may reduce the space available in the pelvis for rotation.
- If the woman requests help or would prefer you to ‘do’ something, there are several techniques you can use to create more space in the pelvis. I have provided a list here. Note that these techniques/positions are about increasing the space in the pelvis rather than rotating the baby – they provide an opportunity rather than making the baby move. And they are interventions.
- Occasionally, despite everything, a baby will become ‘stuck’… and this happens to babies in an OA position too. In this situation, more invasive interventions such as digital rotation (Ray et al. 2018); instrumental birth or c-section may be necessary. However, most of the time, these interventions are carried out due to ‘failure to wait’ rather than a genuinely stuck baby.
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’s wisdom and allow the birth to unfold as it needs to, only intervening if it is truly required.