The presentation of baby in labour is extremely important for how that labour progresses. Most women know, or come to know, through their pregnancy that their baby should be head down in preparation for birth: but even a head-down baby can be in an optimal or suboptimal position depending on where their spine aligns. The baby’s position is important as it affects their ease of rotation and descent as they travel through the birth canal.
The occiput anterior position is the most effective way for the baby to travel down through the pelvis and make its way into the world. The baby is head down, facing the maternal spine which gives space for the chin to be easily tucked in onto their chest allowing the smallest part of their head to fit through the cervix first. The soft bones at the fontanelle fold to make their head smaller still. This position allows the baby to travel through the pelvis as easily as possible. There is less likelihood of a baby in an occiput anterior position needing medical assistance in being born.
The occiput posterior position, while head down, is not so effective at helping the baby on its way through the pelvis. The baby’s spine is aligned with the mother’s such that the baby is facing towards the mother’s naval. As the baby descends they have to rotate all the way around so they’re facing the back, often making the labour longer and more painful, with the pain being felt at the woman’s back caused by the hard surface of the baby’s skull pressing on the mother’s back. It is more difficult for the baby to tuck their chin down, meaning that the diameter of the presenting part of the head is bigger (approximately 11.5cm) than if presenting in an anterior position (approximately 9.5cm).
There needs to be a good connection between the baby’s presenting part and the cervix in labour in order for oxytocin to be released – oxytocin being the stimulus to the uterus contracting. An occiput anterior position allows the best fit of the baby’s head into the cervix, resulting in good contact and hence causing a good flow of oxytocin to be released. When in labour, kneeling positions can encourage this contact by allowing gravity to assist in putting pressure between the baby’s head and cervix. If the baby is in an occiput posterior position, these movements will not be working as effectively for the baby or mother. This can result in a long latent phase of labour for the mother or having a stop-start pattern to contractions.
It was Jean Sutton and Pauline Scott in 1996 who coined the phrase ‘optimal foetal positioning’. Through their work they showed the importance of the mother’s posture and position in pregnancy and labour. They showed that babies who start labour from a left occiput anterior position seem to birth easier. Babies in that position tend to curl the crown of their head into the mother’s pelvis better, allowing a flexed vertex presentation of the skull with a diameter of approximately 9.5cm.
Sutton and Scott noted that the number of left occiput anterior presenting babies are decreasing in recent decades, and attributed this to the change in lifestyle of women. Women are less likely to spend substantial time in active physical housework (often leaning forwards or on all fours) and more likely to spend their time relaxing on laid back sofas. Gravity does the rest in pulling the heaviest part of the baby – its spine – down towards the mother’s spine. By paying particular attention to the encouragement of a left occiput anterior position during the stage of pregnancy where the baby is beginning to start engaging (around 36 weeks for a first time mother and slightly later for biparous or multiparous women) women can help themselves have the most efficient labour possible.
There are ways for women to help position their baby optimally by building in things to their everyday lives. These include: changing their sitting style to ensure their knees are lower than their hips; not crossing their legs; kneel over a birthing ball while watching television; not putting their feet up; sitting on a birth ball not a sofa and swimming using breaststroke or front crawl.
Babies who are right occiput anterior may rotate away from that position as they travel through the pelvis and become posterior during labour. Indeed, Gardberg (1998) states that the majority of occiput posterior babies in labour start off as occiput anterior – likewise the majority of posterior babies will turn in labour too. This, then, would lead to the conclusion that while there is an optimal position to begin labour in, it really isn’t a defining moment for the mother if baby turns away from this position.
 Sutton, J. and Scott, P. (1996) Understanding and teaching optimal foetal positioning. 2nd edn. Tauranga, New Zealand: Birth Concepts.
 Gardberg, M. (1998) Intrapartum sonography and persistent occiput posterior position: a study of 408 deliveries.