18 Sep Left-Occiput-What?

During prenatal visits one of the many things that the midwives do is feel the baby’s position. Some of the things that we are feeling for are where the head is – is it pointed towards the top or bottom of the uterus? – the location of the back, the limbs, what direction the head is facing, potentially where is the placenta? All of these things combined can tell us what position baby is in – especially towards the end of the pregnancy when the baby is larger.

Midwives and other health care professionals refer to baby’s position by specific names such as “LOA” or “ROA” and parents often ask what these letters mean. The basic goals of fetal positioning are to determine if a baby is head down & what side of the mother’s body the baby’s back is on. However, this blog will hopefully break it down into more details for those of you who are interested!

First, what is the vocabulary used to describe fetal positioning? There are six main words or terms used to describe baby’s position:

• Presentation: What fetal part is entering the pelvis (i.e. the head, the butt, a shoulder, or the feet)
• Vertex Presentation: When the fetal head is entering the pelvis first (baby is head down)
• Breech Presentation: When the fetal buttocks, knees or feet enter the pelvis first (baby is not head down)
• Occiput: The back of the skull.
• Anterior: Towards the front of the maternal body (i.e. close to the surface of the belly)
• Posterior: Towards the back of the maternal body (i.e. close to the spine)

Second, how do all of these vocab words come together to form something like “LOA”?

When we talk about fetal position we are talking about what the presenting part is & how it is positioned in the maternal pelvis. The four words used to describe the position in the pelvis are “left”, “right”, “anterior” and “posterior”. If the presenting part is the head, the midwives’ feel for the occiput and the baby’s back. When the occiput is on the mother’s left side and the baby’s back is closest to the mother’s belly the baby is LOA. Occiput on the left, back anterior, thus, LOA.

If the occiput was on the left side of the pelvis but the baby’s back was closest to the mother’s spine it would then be LOP. Occiput on the left, back posterior, thus, LOP. Or, if the occiput was on the right side of the pelvis and the back was closest to the mother’s belly it would then be ROA. Here are some more examples of head down positions (including those listed above):

• ROA: Right Occiput Anterior: Occiput on the right side of the pelvis, baby’s back is closest to the mother’s belly.
• ROP: Right Occiput Posterior. Occiput on the right side of the pelvis, baby’s back is closest to the mother’s spine
• ROT: Right Occiput Transverse. Occiput is on the right side of the pelvis, baby’s back is on the side of the mother’s body -basically, in between anterior and posterior.
• LOA: Left Occiput Anterior: Occiput on the left side of the pelvis, baby’s back is closest to the mother’s belly.
• LOP: Left Occiput Posterior. Occiput on the left side of the pelvis, baby’s back is closest to the mother’s spine.
• LOT: Left Occiput Transverse. Occiput on the left side of the pelvis, baby’s back is on the left side of the mother’s body.
• OA: Occiput Anterior. Occiput is in the central portion of the pelvis, baby’s back is lined up directly central on the mother’s belly.
• OP: Occiput Posterior. Occiput is in the central portion of the pelvis, baby’s back is lined up against mother’s spine.

The above positions all refer to babies who have their chins tucked to their chest and truly have the occiput entering the pelvis first. It is also possible for head down babies to have other presenting parts -such as the face or the brow.

Face presentations occur when the neck is fully extended; the presenting part is the “mentum” or the chin. In these situations the name of the position changes from “LOA” to “LMA” -“Left Mentum Anterior”; which means the mentum is in the left part of the pelvis & the back is closest to mom’s belly. Here are examples of names of positions for face presentations:

• RMA: Right Mentum Anterior. Mentum is on the right side of the pelvis, back is closest to the mom’s belly.
• RMP: Right Mentum Posterior. Mentum in on the right side of the pelvis, back is closest to the mom’s spine.
• RMT: Right Mentum Transverse. Mentum is on the right side of the pelvis, back is on mom’s right side.
• LMA: Left Mentum Anterior. Mentum is on the left side of the pelvis, back is closest to the mom’s belly.
• LMP: Left Mentum Posterior. Mentum is on the left side of the pelvis, back is closest to the mom’s spine.
• LMT: Left Mentum Transverse. Mentum is on the left side of the pelvis, back is on mom’s left side.
• MA: Mentum Anterior. Mentum is in the central portion of the pelvis, back is directly lined up the center of mom’s abdomen.
• MP: Mentum Posterior. Mentum is in the central portion of the pelvis, back is directly lined up against mom’s spine.

Brow presentation occurs when the baby’s head is tipped back about 3/4 of the way to full extension (face presentation). The presenting part is the forehead which is called either the sinciput or the frontum. In these situations the name of the position changes from “LOA” to “LFA” -“Left Frontum Anterior”; meaning the frontum is in the left part of the pelvis and the baby’s back is closest to the mom’s belly. Here are examples of brow presentations:

• RFA: Right Frontum Anterior. Frontum is on the right side of the pelvis, back is closest to mom’s belly.
• RFP: Right Frontum Posterior. Frontum is on the right side of the pelvis, back is closest to mom’s spine.
• RFT: Right Frontum Transverse. Frontum is on the right side of the pelvis, back is on mom’s right side.
• LFA: Left Frontum Anterior. Frontum is on the left side of the pelvis, back is closest to mom’s belly.
• LFP: Left Frontum Posterior. Frontum is on the left side of the pelvis, back is closest to mom’s spine.
• LFT: Left Frontum Transverse. Frontum is on the left side of the pelvis, back is on mom’s left side.
• FA: Frontum Anterior. Frontum is in the central portion of the pelvis, back is directly lined up the center of mom’s abdomen.
• FP: Frontum Posterior. Frontum is in the central portion of the pelvis, back is directly lined up against mom’s spine.

What about non-vertex presentations?

When baby is not head down he or she is breech. There are several variations of breech -complete, frank, single or double footling, and kneeling. It is very common for babies to be breech at some point in the pregnancy. As they grow and prepare for birth we generally expect babies to turn head down around 32 weeks gestation and definitely by 36 weeks. So, for those of you curious about what baby is up to when not head down, here is some information!

• Complete breech: Baby is essentially sitting cross-legged in the pelvis. The sacrum is the presenting part.
• Frank breech: Baby is in a pike position with the legs extended up towards his or her face. The sacrum is the presenting part.
• Single or double footling breech: Baby has one or both feet lower in the pelvis then the rest of the body.
• Kneeling breech: Baby is literally kneeling, the knees are entering the pelvis first.

When a baby is breech and does not have his or her head in the pelvis the position is still named based on what is in the pelvis, which for naming purposes is the sacrum. Though a baby’s feet may be lower than the sacrum the positions are still named based on the location of the sacrum.

• RSA: Right Sacrum Anterior. Sacrum is on the right side of the pelvis, back is closest to mom’s belly.
• RSP: Right Sacrum Posterior. Sacrum is on the right side of the pelvis, back is closest to mom’s spine.
• RST: Right Sacrum Transverse. Sacrum is on the right side of the pelvis, back is on mom’s right side.
• LSA: Left Sacrum Anterior. Sacrum is on the left side of the pelvis, back is closest to mom’s belly.
• LSP: Left Sacrum Posterior. Sacrum is on the left side of the pelvis, back is closest to mom’s spine.
• LST: Left Sacrum Transverse. Sacrum is on the left side of the pelvis, back is on mom’s left side.
• SA: Sacrum Anterior. Sacrum is in the central portion of the pelvis, baby’s back is directly central on mom’s abdomen.
• SP: Sacrum Posterior. Sacrum is in the central portion of the pelvis, baby’s back is lined up against mom’s spine.

Another possible presentation for baby to be in is called “transverse”. This occurs when the baby’s spine & the mother’s spine essentially are making a right angle. Rather than having the two spines parallel to one another (either head down or breech) the spines are perpendicular. Baby is lying across the top of the pelvis. Transverse can be a common position for babies to be in early on in pregnancy -at term and during birth the rates of transverse positioning are much lower (about 1 in 500 according to Anne Frye, Holistic Midwifery Volume 1). In this position the most common presenting part is the shoulder (specifically the tip of the scapula), or “acromion”. For example, RAA would be Right Acromion Anterior; meaning the the shoulder is in the right portion of the pelvis and the back is closest to mom’s belly. Either the right or left shoulders can present in either the anterior or posterior positions. It is also possible to have the extremities, followed by the belly to be the first things entering the pelvis when in a transverse lie. This is called “LAS” or “RAS” and means either the left or right acromion (shoulder) is superior (above the rest of the body). It is also possible to have the opposite of a “belly presentation” and that would be the baby’s back presenting into the pelvis first. This position is called “LAI” or “RAI” and means left or right acromion is inferior (below the rest of the body). Typically, when babies are in transverse lies earlier in pregnancy they are so small that not all midwives can discern which parts are which and they simply may be “transverse” rather than the more detailed names listed above.

So, what is the optimal position for baby to be in at the time of birth?

First off, we would like baby to be head down. The head is really good at putting pressure on the cervix and helping it to dilate evenly all around. Secondly, we would like baby to be anterior (back close to mom’s belly). When a baby is anterior he or she can really tuck his chin to his chest and overall fits through the pelvis and birth canal best in this position.

Vaginal birth can occur with the majority of the head down positions listed above and with some of the breech positions listed as well. Of course, some of the positions come with different risks or things to be aware of. In the event that your baby is in a position that is considered to be a variation of normal please discuss your options with your care provider.

Please remember that throughout your pregnancy -especially the first and second trimesters- baby is very mobile. Your baby may be head down one day and then transverse or breech the next day! That’s absolutely okay. We’d like to see baby’s turn head down around 32 weeks and then stay there but there are many things we do to help encourage a baby to turn if need be. Baby’s and mom’s have a great deal of wisdom and it’s totally okay for babies to be moving all over before going and staying head down. If you are looking for ideas on how to help baby be in the best position for birth, check out Spinning Babies.