What is a posterior fetal presentation? Why would a baby’s posterior position matter in labor? Here are pregnancy clues a mother can use to tell if baby is sunny-side up.
I explain why some posteriors are easy, while others are long and painful, and how to tell which labor it’s going to be. After this, you might go to What to do when….in Labor.
What does it mean to have a posterior baby?
The OP position (occiput posterior fetal position) is when the back of baby’s head is against the mother’s back. Here are drawings of an anterior and posterior presentation.
Look at this drawing. The posterior baby’s back is often extended straight, even arched, along the mother’s spine. Having the baby’s back extended often pushes the baby’s chin up.
Having the chin up is what makes the posterior baby’s head seem larger than the same baby when it’s in the anterior position. Because the top of the head enters (or tries to enter) the pelvis first, baby seems much bigger by the mother’s measurements.
A posterior head circumference measures larger than the anterior head circumference.
The difference can make a woman’s labor pattern vary. Compare anterior and posterior labor patterns.
A posterior presentation aims the top of the head into the pelvis, i.e. oblong, rather than the circle of the crown. The anterior baby’s head enters the pelvis from the crown of the head first. The crown molds more easily.
There are four posterior positions.
The direct OP is the classic posterior position with the baby facing straight forward.
Right Occiput Transverse (ROT) is a common starting position in which the baby has a bit more likelihood of rotating to the posterior during labor than to the anterior. Right Occiput Posterior usually involves a straight back with a lifted chin (in the first-time mother).
Left Occiput Posterior places the baby’s back opposite the maternal liver and may let the baby flex (curl) his or her back and therefore tuck the chin for a better birth. These are generalities, of course.
Pregnancy may or may not show symptoms
Just because a woman’s back doesn’t hurt in pregnancy doesn’t mean baby is not posterior.
Just because a woman is quite comfortable in pregnancy doesn’t mean baby is not posterior.
A woman can’t always feel baby’s limbs moving in front to tell if baby is facing the front.
Baby’s posterior position may matter in labor
With a posterior presentation, labor may or may not be significantly affected. There is a spectrum of possibilities with a posterior baby.
Some women will not know they had a posterior baby because no one mentions it. Either the providers didn’t know, or didn’t notice. If labor moved along, they may not have looked at fetal position clues since there was no reason to figure out why labor wasn’t progressing. If a woman didn’t have back labor (more pain in her back than in her abdomen), the provider may not have been “clued into” baby’s position.
Some posterior babies are born in less than 8 hours and position did not slow down labor.
Some posterior babies are born in less than 24 hours and position did not slow down labor enough to be out of the norm.
Some posterior babies are born in less than 36-48 hours without the need for interventions.
Some posterior labors are manageable when women are mobile, supported and eat and drink freely, as needed.
Some posterior labor need extra support that a well-trained and experienced doula may provide, but that typically a mate or loved one would not have the skills or stamina to keep up with the demands of the labor.
Some posterior labors progress only with the help of a highly-trained pregnancy bodyworker or deep spiritual, or otherwise non-conventional, model of care. Or, they seem only able to finish with medical intervention.
Some posterior labors are served by an epidural, meaning the pelvic floor relaxes enough for baby to rotate and come out.
Some epidurals, on the other hand, make it so that a woman can not finish the birth vaginally.
NOTE: Parents should know — some birth researchers, like Pediatrician John Kennell, are seriously asking whether a mother’s epidural turns off her body’s release of pain-relieving hormones which a baby relies on during childbirth.
Some babies can’t turn and can’t be born vaginally and must be born by cesarean.
This is a spectrum of possibilities. I’ve seen every one of the above possibilities several times and can add the wonderful experience of seeing a woman laughing pleasurably and squatting while her posterior baby slid out on to her bedroom floor.
Possible posterior effects, some women will have one or two and some many of these:
- Longer pregnancy (some research shows this and some doesn’t)
- The amniotic sac breaking (water breaks, membranes open, rupture of membranes) before labor (1 in 5 OP labors)
- Not starting in time before an induction is scheduled
- Labor is longer and stronger and less rhythmic than expected
- Start and stop labor pattern
- Baby may not engage, even during pushing stage
- Longer early labor
- Longer active labor
- Back labor (in some cases)
- Pitocin may be used when labor stalls (but a snoring good rest followed by oatmeal may restore a contraction pattern, too)
- Longer pushing stage
- Maybe a woman has all three phases of labor lengthened by the OP labor, or one or two of the three phases listed.
- Sometimes the baby’s head gets stuck turned half way to anterior – in the transverse diameter. This may be called a transverse arrest (not a transverse lie).
- More likely to tear
- More likely to need a vacuum (ventouse) or forceps
- More likely to need a cesarean
Who might have a hard time with a posterior baby?
- A first-time mom, or
- A first-time mom whose baby hasn’t dropped into the pelvis by 38 weeks gestation (two weeks before the due date).
- A woman with an android pelvis (“runs like a boy,” often long and lanky, low pubis with narrow pubic arch and/or her sitz bones are close together, closer than or equal to the width of a fist).
- A woman whose baby, in the third trimester, doesn’t seem to change position at all, over the weeks. He or she kicks in the womb and stretches, but whose trunk is stationary for weeks. This mother’s broad ligament may be so tight that she may be uncomfortable when baby moves.
- A woman who has an epidural early in labor (data supports this), before the baby has a chance to rotate and come down.
- A woman who labors lying in bed
- Low thyroid, low-energy woman who has gone overdue (this is my observation)
- A woman who lacks support by a calm and assured woman who is calming and reassuring to the birthing mother (a doula)
- A woman put on the clock
- A woman who refuses all help when the labor exceeds her ability to physically sustain her self (spilling ketones, dehydration, unable to eat or rest in a labor over X amount of hours which might be 24 for some or 48 for others)
- A woman whose birth team can’t match an appropriate technique to the needs of the baby for flexion, rotation, and/or descent FROM THE LEVEL OF THE PELVIS WHERE THE BABY IS CURRENTLY AT WHEN STUCK.
Who is likely to have an easy time with a posterior baby?
- A second-time mom who’s given birth readily before (pushing went well)
- A posterior baby with a tucked chin on his or her mama’s left side with a round pelvic brim
- An average-sized or smaller baby
- Someone whose posterior baby changes from right to left after doing inversions and other balancing work, though the baby is still posterior
- A woman with a baby in the Left Occiput Posterior, especially if the baby’s chin is tucked or flexed
- A woman who gets body work, myofascial release, etc.
- A woman whose posterior baby engages, and does not have an android (triangular) pelvis or a small outlet.
- And of all of these, what is necessary is a pelvis big enough to accommodate the baby’s extra head size.
- A woman who uses active birthing techniques; vertical positions, moves spontaneously and instinctively or with specific techniques from Spinning Babies and other good advice.
- A woman in a balanced nervous state, not so alert and “pumped up,” on guard, etc.
Other women may also have an easier time than public opinion might indicate, too, just because she isn’t on this list. Equally, just because she is on the “hard” list, it doesn’t mean she will have a hard time for sure.
These are general observations. They are neither condemnations nor promises.
Overall, some posterior babies will need help getting born, while some posterior babies are born easily (easy being a relative term).
Let’s not be ideological about posterior labors.
While most posterior babies do eventually rotate, that can still mean there is quite a long wait -and a lot of physical labor during that wait. Sometimes it means the doula, midwife, nurse, or doctor is asking the mother to do a variety of position changes, techniques, and even medical interventions to help finish the labor.
Patience works for many, but for some a cesarean is really the only way to be born.
Read What To Do When…in Labor.
What causes a baby to be posterior?
There is a rising incidence of posterior babies at the time of birth.
We know now that epidural anesthesia increases the rate of posterior position at the time of birth from about 4% (for women who don’t choose an epidural in a university birth setting) up to about 13% when an epidural is used (Lieberman, 2005).
Low thyroid function is associated with fetal malposition such as posterior or breech. (See Research & References.)
Most babies who are posterior early in labor will rotate to anterior once labor gets going. Some babies rotate late in labor, even just before emerging. Studies, such as Lieberman’s, show that at any given phase of labor, another 20% posterior babies will rotate so that only a small number are still posterior as the head emerges.
My observations are that the majority of babies are posterior before labor. The high numbers of posterior babies at the end of pregnancy and the early phase of labor is a change from what was seen in studies over ten years old. Perhaps this is from our cultural habits of sitting at desks, sitting in bucket seats (cars), and leaning back on the couch (slouching). Soft tissues, such as the psoas muscle pair or the broad ligament, also seem to be tight more often from these postures, from athletics (quick stops, jolts and falls), from accidents and from emotional or sexual assault.
Being a nurse or bodyworker who turns to care for people in a bed or on a table will also twist the lower uterine segment (along with some of the previously mentioned causes). This makes the baby have to compensate in a womb that is no longer symmetrical.
Less often, the growing baby settles face-forward over a smaller pelvis, or a triangular-shaped pelvis (android). At the end of pregnancy, the baby’s forehead has settled onto a narrower than usual pubic bone, and if tight round ligaments hold the forehead there, the baby may have a tough time rotating.
These are the moms and babies that I’m most concerned with in my work at Spinning Babies.
A baby that was breech beyond week 30 -34 of pregnancy will flip head down in the posterior position.
A woman with a history of breech or posterior babies is more likely to have a breech or posterior baby in the next pregnancy. However, she may not have as long a labor.
The best way to tell if your baby is OP or not, usually, is if you feel little wiggles in the abdomen right above your pubic bone. These are the fingers. They’d feel like little fingers wiggling, not like a big thunk or grinding from the head, though you might feel that, too.
The little fingers will be playing by the mouth. This is the easiest indication of OP. The wiggles will be centered in the middle of your lower abdomen, close to the pubic bone.
If you feel wiggles far to the right, near your hip, and kicks above on the right, but not near the center and none on the left, then those signal an OA or LOT baby (who will rotate to the OA easily in an active birth).
After this, you might go to What to do when…in Labor.
Check out our current references in the Research & References section.