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Ronnie Falcao, LM MS, a homebirth midwife in Mountain View, CA

Cord Entanglement as Possible Cause of Posterior Presentation

About a persistent posterior position:

You know, there's a nagging little voice in my head that moves me to mention the possibility of cord entanglement. This comes to mind both because the baby keeps turning back and because you mentioned the possibility of a hand above the head, which is sometimes held in place by the cord.

Cord entanglement, in and of itself, is not usually a big deal. It's very common - the cord is wrapped around the baby in one way or another in about a third of births, and it rarely presents a real problem. So, I want to make sure that my mentioning this doesn't cause anxiety for you. I mean it to be a piece of information that might be useful to you as follows.

There are some configurations of cord entanglement where the cord is wrapped around the baby's arms snugly enough that when the baby moves its arms, the cord shortens and the baby turns (because of its attachment to the cord at the umbilicus). This same phenomenon can happen as the baby descends away from the placenta, also shortening the cord and causing the baby to turn as it descends, in an unusual way. This kind of cord entanglement can inhibit engagement in a nice, anterior position.

This requires a great deal of sensitivity on your part, but it might be worth your while to try getting the baby to roll in the opposite direction to an anterior position to see if there's some cord that might get unwound that way. Most moms tend to get up and down in one particular direction, and I'm guessing that the baby tends to turn back and forth on one particular side. (If this latter point isn't the case, then it's unlikely there's any significant cord entanglement and you can ignore this whole section.)

Anyway, if you can get a doll and play around with wrapping it in an umbilical cord, you can try modeling what might be happening with this baby. This is all a very big "if", but I thought I should mention it to you.

This was more of an observation than anything else. We began noticing that many of the women whose babies started in the ROA position before labour then experienced long hard labours with back pain and thge baby turned from ROA to ROP to LOP to LOA before strong active labour started. We also noticed that if a woman had a baby lying ROA and was induced or had her membranes ruptured she was significantly more likely to have a caesarean for lack of progress/CPD/maternal exhaustion than if the baby was LOA when these procedures were done.

I observed several births where the baby was ROA and particularly active in the days before labour was induced. An induction was done and it was found after many many hours of intermittent and irregular contractions with little or no change in the cervix that the baby had moved to ROL or ROP and then a caesarean was carried out.

So, my theory. I believe there is some physiological reason why a baby needs to enter the pelvis from an LOA rather than a ROA position. I have asked many why this might be including my university lecturer who passed my enquiry onto the head professor of the science faculty, Sheila Kitzinger and my osteopath who asked his professor in the UK from when he was studying. No-one seems to know - most have never even heard that this is likely. My osteopath had a theory that there is something about the shape of the ligaments in the pelvis that form a tunnel to guide the baby through that makes an LOA position more favourabler - especially if the pelvis/baby's head size is a tight fit.

One of the things I ask my mums now when they are having their last few antenatal appointments with their doctor is whether the baby is LOA or ROA if lying anterior. If ROA then I find they usually say the baby is very very active in the last few days - trying to move to a better position? I then suggest they swim and do a few somersaults to allow the baby to move out of the pelvis a little and hopefully turn then. If already in labour, I get them to lie on their right sides to move the baby round their right hip. Once they start to experience back pain I then get them to lie on their left side until the baby is clearly lying directly posterior or is lying LOP. Then onto all fours. I don't suggest all fours with an ROA baby since it is then less likely to turn to ROP and make that full turn. It just sits there instead and doesn't move.

If the baby moves to posterior during this time, the contractions often then become irregular. They may be comeing every 3-5 minutes but they are lasting for different lengths of time and often different intenstities. This I believe is because of the effect of the uneven pressure being exerted by the baby's head n the cervix. Now I'll try my explanation of this - get your doll ready!

Hold the baby in an anterior position curled up with the head down. Imagine the contraction starting - it starts from a pacemaker in the top of the uterus and moves downwards over the baby's body. It will move down over the baby's back and over the back of the baby's neck. As it moves over the baby's neck it encourages the baby's head to become more flexed - tucked more into its chest. Now the part of the head that is sitting directly over the cervix is the occiput or back of the head. Look at this shape - it is perfectly round and fits nice and snugly over the cervix. If there is nice even and consistent pressure on the cervix the reflex that stimulates the release of more oxytocin is greater. Now more oxytocin is generated, causing stronger contractions.

Now turn the baby around to LOP. The contraction now moves over the baby's tucked in legs and onto the chin, forcing the head to become more extended (bent back at the neck). Now look at the part of the head presenting over the cervix. Not the same shape as the cervix and it will sit slightly to one edge of the cervix. No consistent even pressure therefore not as strong an effect on the reflex to release oxytocin. Also, more likely to end up with a lip even if labour does progress since part of the cervix has less pressure on it than another part.

Most of the women we work with practice and are taught optimal fetal positioning. Very very rarely will we see directly posterior babies before labour starts. But we do still see quite a few babies starting on ROA. Sitting forwards and practicing optimal fetal positioning will not help these mothers unless the baby is going to stay ROA - rare in our experience. This is why I encourage them to swim to get that baby to move to posterior then start optimal fetal positioning (especially hands and knees) to encourage it to turn LOA.

To envisage the effect of the occiput on the cervix - take an orange and a glass. Imagine the orange is the baby's head and the glass the cervix. Place the glass upright on a table and sit the orange on top - it sits perfectly and exerts even pressure. Now tilt the glass backwards or lie it down - the orange cannot exert even pressure. Shows the impartance of upright positions.Do the same now with a glass and a lemon. A lemon is more the shape of the presenting part with a posterior baby. See how it does not fit evenly - shows the effect of posterior versus anterior positioning. I use this visual aid in classes for clients to see the effects.

In case anyone asks, how can you tell if the baby has moved from ROA to posterior without vaginal examinations or palpating the mum's tummy?

ROA - A baby lying ROA the mother may not be able to feel distinct kicks. If you look at her tummy from the front you can see her tummy leans to the right.

ROL - she will feel more pain in her right hip rather than anywhere else. If you look at her hips you will often see the right hip is sticking out more than the left.

ROP - The mother may be feeling kicks at the front of her tummy, to the left of her tummy button. There may be the distinct dip in the tummy button area or if she lies flat on her back her tummy may be very flat looking in the middle.

Direct posterior - as the baby moves over the sacrum the sacrum will move out - you can feel it go out under your hand. A dark line from then crack of her bottom up her back a few inches appears - you don't normally see this unless the mother is almost fully dilated but it is also there if the baby is directly posterior. If directly posterior the line will fade again after the baby turns to anterior.

LOP - now the kicks are felt to the right of the tummy button. The back will ache more on the left than anywhere else. The flat rummy or dip is still there.

LOL - the left hip begins to stick out more and it hurts more in this area than anywhere else.

LOA - now the tummy is sloping towards the left, the dip has disappeared and the back pain usually gone. More intensity is felt in the lower pubic area at the front than there is in the back.

I had a mum last week who went through this pattern perfectly. Wierdly I could feel the baby's heartrate under my hand as the baby moved to direct posterior - some may be very skeptical about this. I was applying sacral pressure to help with the back pain and started to notice a regular beat under my hand - very faint. I checked the mums pulse and this was much faster. I then started timing it and found it was a regular beat of about 145 beats per minute. Don't know for certain but this was the best explanation I could think of. As the baby turned from LOL to LOA I felt her bottom slide under my hand just beside the mum's left hip, then I felt her arm and then slowly her back. Great birth!

Lots of what I write here is just from my observations. I've looked in the literature, but haven't found much about this.  Obstetricians often don't care to look at those things which can be fixed by "just doing a cesarean".

Some of what I write here is from "Optimal Foetal Positioning".

I don't know the stats exactly, but I think about 70% of babies start labor LOA.  The reason is pretty simple: the torso is not symmetric.  The left side has a descending colon, which takes up space that would otherwise be baby's playground. When the baby tucks the back in on the left side, then baby has more room to kick and stretch the legs on the right side without running into things that will change the position. If baby ends up with the back on the right side, the kicking is going to run into the colon and give the baby some "purchase" to move around to the other side.

So, all other things being equal, babies prefer LOA.

In addition, the descending colon acts as a buttress to keep an LOA baby from rotating posterior, so it's unusual to see an LOA baby rotate posterior during labor, but I did see this once with a baby that was stuck there, held by cord.

So . . . why would babies start labor ROA?  I work hard in my practice to encourage babies over onto the left side and/or to feel that I have a good understanding of why they're doing what they're doing (fibroids?  mom sleeps on right side?).  But this is what I've noticed with a few babies that get "stuck" on the right side.

As babies grow larger in pregnancy, they take up more room and can no longer easily rotate the back through the posterior arc, i.e., they can easily move the back from side to side across the front of the mom's belly, but not around the inside - the "back" side.  They may get "stuck" in an ROA position by a loop of cord around the neck which prevents them from rotating across the front of the mom's belly to the LOA position, which they would prefer.  When the contractions start to force them lower into the pelvis, they have to "unwind" from the umbilical cord by rotating posterior, which may become easier as the contractions mold the head so it can rotate in the pelvis, and the baby may have more room up top to tuck the legs so they can rotate the body.

As a midwife, I listen very closely to what moms say about baby movement around 32-34 weeks.  Lots of them report lots of baby movement across the front of the belly.  This tells me that whichever side they actually start labor on, they have enough play in the cord to make the forward rotation and descent necessary for birth.  If a mom tells me that the baby really seems to like one side or the other and hasn't moved in weeks, then we can play around with her position to see if baby moves easily to get the back over onto the other side.  If not, I get the mom in a knee-chest position so any loose cord will fall away from the pelvis, and then I use my Doppler to listen for cord around the neck.

At 32-34 weeks, it is still relatively easy to get the baby to do an inside rotation to unwind enough cord so they're not stuck in any particular position anymore.  For all the U/S's being done these days, you'd think cord around the neck would be an issue of the past.  Sigh.