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 his back towards his mothers back. The back of the baby’s head is referred to as the ‘occiput’ and is in the back of the pelvis 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 position.
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. I find it is 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 her 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 her head is in the cavity she can rotate. The downward pressure of the contractions, and the tension and shape of the pelvic floor will guide her into a direct occipito anterior (OA) position and through the outlet. 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 her 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‘.
It is difficult enough for a woman with a baby in an OA position to fit prescribed patterns of labour progress. A baby who enters the brim in an OP position may not fit quite so snuggly on the cervix and this may lead to:
- ‘post-dates’ pregancy
- rupture of membranes before labour
- a long stop-start build up to labour
- irregular contractions during labour
- slower cervical dilation while rotation takes place (and often very quick once baby rotates)
These situations only become problematic when we apply generalised expectations about how labour should be to an individual woman, baby and situation. The solution is often to augment labour with syntocinon – increasing the risk of fetal distress and increasing pain ie. creating a problem. Another solution is to encourage the woman to get into various positions to assist with rotation. However, the use of prescribed positions to ‘fix’ an OP position is not supported by research (Desbriere et al. 2012; Science & Sensibility).
Pain and interventions
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 back ache in labour, whilst many with an OP baby do not. Unfortunately, women are told that an 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 pursuaded 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 less likely to meet prescribed progress timeframes, and therefore, have her labour induced or augmented by ARM and/or syntocinon (pitocin). An ARM reduces the fluid surrounding the baby, making rotation more difficult, and increases pain. Syntocinon increases the risk for mother and baby in many ways, and increases pain. These interventions further increase the chance that an epidural will be needed. 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 rotate him. In addition, the pelvic floor is anaesthetised and loses it’s tone, taking away the resistance that assists rotation.
Early urge to push
As the OP baby descends through the pelvis the back of his 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 floor – the baby is able to pivot against this tension. However, this urge to push is managed as a problem, and the result is often an epidural. See this post about pushing before full dilatation of the cervix.
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!
We need to stop defining OP as a problem or a ‘malposition’. It is a common variation to the more common OA position, and the OP baby is probably in that position for a good reason. When caring for a woman with an OP baby:
- 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.
- She can try a variety of techniques to encourage the baby to turn (even though the research suggests it may be ineffective). You can find some suggestions here. However, if he doesn’t respond it’s because he has chosen his optimal position for labour. He will turn once he gets into the pelvic cavity in labour, or he may even be born OP.
- Tell her 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 rotate her.
- Don’t tell her not to push if she is spontaneously pushing – regardless of cervical dilatation.
- Back pain can be relieved by: a forward leaning position (Stremler et al. 2005); warm water; sterile water injections; gentle sacral pressure. 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 a number of 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.
- 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 (Reichman et al. 2008); instrumental birth or c-section may be necessary.
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 her journey through her mother’s unique body. After all, she has more knowledge about the interior of her 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.
You can download a review of research relating to ‘management’ of OP by Simkin (2010) here.