We've discussed briefly before that belly shape can tell you a lot about the position of your baby before birth.
Now let's get into specifics about fetal position, how it can influence labor and birth, and why it is so relevant for women of size in particular.
Anterior vs. Posterior
The classic big round "basketball belly" usually means that the baby is anterior. The back of the baby's head ("occiput") is towards the mom's front (which is why the position is called Occiput Anterior or OA), and the baby's eyes are looking towards the mama's back.
Look at the picture below and notice that the mother's belly looks big and well-rounded. This is because it is following the curve of the baby's back (and later, when the baby's head engages, its bottom).
Generally speaking, occiput anterior is the ideal position for birth. As long as the baby's head is lined up well, there are no arms/hands in the way, and it tucks its chin, chances are that the birth of an anterior baby will progress smoothly, especially if labor is allowed to start spontaneously.
Obviously there are exceptions, but research supports that anterior babies have more normal, uncomplicated labors and vaginal births than other positions.
A lumpy, bumpy, not very noticeable belly (especially one with a curved-in spot around or near your belly button) often means that the baby is posterior. Look at the picture below and notice how the belly is not as rounded and has a "dip" below the belly button.
In this position, the back of the baby's head (occiput) is towards the mother's back, so the position is called Occiput Posterior or OP, but most people think of it as the baby facing up, towards mama's belly ("stargazing").
This is usually a much harder position for birth because the diameter of the baby's head in OP is larger and doesn't slip through as easily, and because pressure on the cervix tends to be uneven and so labor progresses more slowly.
Go back and compare the two pictures above again. Notice again the difference in the shape of the mother's belly. The anterior baby belly is more rounded, while the posterior baby belly is more lumpy and bumpy and has a concave area just below the belly button.
Other Differences Between Anterior And Posterior
There are other differences between an anterior and posterior baby too. These include where the mother feels the baby's movements most strongly, how "pregnant" she looks, and clinical signs such as where the fetal heartbeats are found, etc.
With a posterior baby, often the mom feels lots of weird, fluttery movements in front (the baby's hands and feet). Mom usually feels a lot of movement, pretty consistently, and feels it quite strongly.
With an anterior baby, most movement is usually felt in the upper right-hand quadrant of the belly (or upper left-hand quadrant sometimes), and while she certainly feels her baby's kicks and movements, the feeling may not be as strong or as constant as with a posterior baby.
With a posterior baby, people often comment the mom doesn't "look" very pregnant. The belly is not as rounded and doesn't stick out nearly as much.
With an anterior baby, the mom looks much more pregnant. She usually has a more rounded "basketball" belly, and it sticks out amazingly far, like she is ready to go into labor at any minute.
The mother can have the same size baby but look totally different day to day if baby shifts position, and will look a lot less pregnant when baby is posterior than when baby is anterior.
Fetal Heart Tones
Clinically, there are a few other signs as well. With a posterior baby, fetal heart tones are usually more difficult to locate because the baby's back is away from the front of mom's belly. Clinicians usually have to search for the heart tones for a while before they find them and the tones may appear and disappear with even small shifts in the baby's position.
With an anterior baby, fetal heart tones are more easily located because the baby's back is up against the mom's belly. Heart tones are most typically found in the lower left-hand belly area, and they usually stay audible pretty well, even as the baby shifts a bit.
Now, please note....fetal position is not that important until near term. Babies need to exercise like anyone else, and they will flip and turn and rotate and surf all through pregnancy until near term when they get too big to do so much gyrating. So before close to term, fetal position is not really something to be all that concerned about. Babies flip around a lot and it's no big deal.
However, if near term (getting near 37+ weeks), you consistently don't "look" pregnant, you tend to feel baby's movement all up front, you tend to have a concave belly around the belly button, and your birth attendant consistently has a difficult time finding the baby's heartbeat (and doesn't usually find it on the lower left-hand side of your belly).....you may have a persistently posterior baby.
If so, it may behoove you to see if you can influence your baby's position before labor. More on that later.
Why Fetal Position is Relevant
Although babies do shift their positions a lot in pregnancy and labor and it's important not to obsess too much about fetal position, a baby that consistently stays in a posterior position can be a cause for concern.
Labor with a persistently posterior baby tends to be longer, harder, and more painful than with an anterior, well-aligned baby. Furthermore, because posterior labors tend to be longer and more painful, they often have more interventions associated with them (breaking the waters, artificially strengthening contractions with pitocin, epidurals for the pain, more vacuum extractions, etc.), and babies may experience fetal distress more often.
As a result, most research shows that the rate of cesareans associated with persistent posterior babies is much higher than the rate associated with anterior babies. In one 2006 study, researchers found that a persistent posterior position was associated with 13 times the risk for cesarean section.
Thus a persistent posterior fetal position can be a cause for concern late in pregnancy, and awareness of fetal position may be important.
Fetal Position and "Obesity"
Fetal position is particularly relevant to women of size. Although no one has studied the issue of fetal position in "obese" women really conclusively, some recent research does show a higher rate of persistent posterior babies in "obese" women. (More details on that later.)
Older research (from the 50s, 60s, and 70s, when they paid more attention to fetal position), also sometimes noted a higher rate of malpositions (especially posterior) in "obese" women.
Anecdotally, my own birth stories and the birth stories of many fat women I've received over the years for my website seems to support the idea of a higher rate of malpositions as well. This may be one reason (among many) why our cesarean rate is higher (especially for "CPD" or babies that don't "fit" well).
More on how fetal position affects labor in the next post, and later, what you can do to try and encourage good fetal position before and during labor.