In this article, what is a posterior fetal position, pregnancy clues a mother can use to tell if baby is posterior, why it matters in labor, who might have an easy posterior labor and who might need more help. Click to go to What to do in a Posterior Labor.
Pregnancy may or may not show symptoms - labor may or may not be significantly effected. When labor IS effected, there is a range of what can happen.
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 presentation and a posterior presentation.
Look at this drawing. The anterior baby can more easily tuck his or her chin. The posterior baby's back is extended or arched along the mother's spine, because the spine curves forward in the mother's lower back (the drawing doesn't show that). But having the baby's back extended often pushes the baby's chin up. Posterior babies more often have an extended neck. Read more about flexion.
Even if the chin is tucked, the posterior head still seems larger than when in the anterior position. This is because the posterior head circumference measures larger than the anterior head circumference.
A posterior presentation aims the top of the head into the pelvis, like an 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. The anterior baby's head measures smaller than the posterior baby's head when coming through the pelvis.
The difference can make a woman's labor pattern vary. Compare Anterior and Posterior labor patterns.
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 to rotate 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.
See more about other posterior positions in Belly Mapping in this section.
There are a spectrum of effects possible with a posterior baby.
The same effects do not happen to all women. First let's look at the effects of a posterior fetal position and then we'll try and figure out who is likely to have which effects.
Possible posterior effects range from
- Longer pregnancy
The amniotic sac breaking (water breaks, membranes open, rupture of membranes) before labor
Start and stop labor pattern
- Longer early labor
- Longer active labor
- 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.)
- More use of vacuum or forceps
- More likely to tear
- Sometimes the baby's head gets stuck turned half way to anterior - in the transverse diameter. This can be called a transverse arrest. It is not a transverse lie
- More likely to need a cesarean
These effects are in comparison to a baby in the left occiput anterior or left occiput transverse fetal position at the start of labor.
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 in bed
- Low thyroid, low energy woman whose gone overdue (observation, not data)
- 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 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 in a mama with a round pelvic brim
- An average size or smaller baby
- Someone who's 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 she also 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.
Other women may also have an easier time than public opinoion might indicate, too, just because she isn't on this list, orjust because she is on the "hard" list, doesn't mean she will have a hard time for sure. These are general observations, but are not either condemnations nor promises.
So, some posterior babies will need help getting born, some posterior babies are born easily (easy being a relative term).
Let's not be ideological about posterior labors:
Here is a YouTube video of a spontaneous, hands-off birth with the baby in the direct Occiput Posterior position. The baby is wiggling, in my estimation, to work the shoulders out of the transverse diameter into the oblique. While some babies will need help when the shoulders are "sticky", this baby was able to do this independently. The baby's expression showed that the baby was doing well and we see that in the good muscle tone upon birth. The whiteness of the baby is from the unusually thick vernix (natural fetal skin lotion to protect babies from getting prune skin in the water they live in) and the lighting. Her nostrils look a little funny because her nose is coated with vernix! Film by www.midwifepriscilla.com
However, a large minority of women with a posterior baby will need help with the birth.
While most posterior babies do eventually rotate, that word eventually can 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 herself, 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.
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)
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 such posture, from athletics (quick stops, jolts and falls), from accidents and emotional or sexual assault.
Being a nurse or body worker 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 make s 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, 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, even so.
She's a busy little thing and still breech. I've delivered a posterior baby and don't want the birth of a breech baby on my resume too! So I'm praying that she'll get into the head down-face down position! -
I'll be adding references to this article in the future. you can email me for a reference sheet and bibliography. Read the 3 Principles next.
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 signals go with an OA or LOT baby (who will rotate to the OA easily in an active birth).