The baby's head is the largest
part of his or her body, so when a baby delivers head-first, it usually
follows that...well... the rest of the baby follows. But there are many
variations from the standard head-first descent of the presenting part,
like breech, transverse, shoulder-first,
etc. Even among the head-first deliveries, the face can be pointing down
or up, or even face-first. It's these little surprises that keep an obstetrician
or midwife on alert with each seemingly "routine" delivery.
In the head-first category, the shape of the
mother's pelvis can determine which way the head is placed. The most common
way is face-down (Occiput Anterior),
and this allows the easiest measurement to clear the pelvis. This position
is especially helpful because the head can pivot up against the pubic bone,
allowing the chin's appearance to finish the delivery of the full head.
Face-up, called Occipital
Posterior (back of the head down), is a more difficult delivery
because the baby can't flex the head on exit. It's like delivering a baby
a pound bigger. It's not impossible, but it's more difficult to push with
effectiveness, and the pushing stage of labor can last longer than usual.
If the head is sideways, then the rotation necessary for delivery is incomplete.
Called "Occiput Transverse,"
the head can usually be gently rotated by the obstetrician to face-down
(Occipital Anterior) for a normal delivery.
Asynclitism
is a word that describes a head-first position wherein the head is
tilted to the right or left from the midline. Many people feel that an
epidural given before the head has descended well into the pelvis causes
the maternal muscles that normally guide the head down correctly to get
relaxed, resulting in a sloppy, unguided descent. It's a hard positioning
to work with and can lead to the need for C-section.
And then after all of the head-first positions,
there's every other way.
Breech refers
to feet- or buttocks-first presentation. This is a real thinking obstetrician's
dilemma, because, as mentioned above, the largest part of the baby is the
head. So delivery of the feet or buttocks creates a scenario wherein larger
and larger parts of the baby have yet to prove the ability to clear the
pelvis. In other words, if the head won't fit out in a head-first baby,
delivery can be effected via second-choice¡Vthe
C-section. But in a breech delivery, if the
head won't fit out, the rest of the baby already has. The cord
is out as well and is compressed in the birth canal on it's way up
to the placenta. This is such an emergency with such a bad outcome that
most obstetricians feel that
breech = C-section.
But why do some babies come out head first ("vertex"
presentation) and some breech?
Babies tend to seek the most comfortable position
in their mothers' wombs (uteri). If the largest part of the baby is the
head, then over time the baby will fidget and maneuver around until the
head gravitates to the largest space in the uterus. That most generous
space is the lower uterine space. And usually at 32 weeks this position
will stick.
So a breech, by the laws of physics, will be
in such a position if there's some problem with the lower uterus NOT being
the biggest space. For instance, a low-lying placenta or placenta previa
can occupy enough space so that the biggest space is up high. Also, congenital
abnormalities can make other parts of the baby the biggest part, meaning
THAT part will become the lowermost presenting part. In fact, in my training
it was always a warning to check for abnormalities when there was a breech
presentation.
In a
"frank breech," the buttocks are first.
In a "footling" breech, one or both feet are first the "single
footling" breech and the "double footling"
breech. The difference depends on whether the knees are bent or not. In
both, the hips are flexed, but if the knees are straight, then the lower
legs, along with the thighs, are bent over the baby's abdomen, resulting
in the frank breech. If the knees are bent, then the feet are positioned
back toward the cervix and the outside world.
Thankfully, most breeches are in that position
for, officially, "unknown" reasons. Mostly normal breech babies are delivered
by C-section, putting to rest the fear of congenital
problems. Some brave obstetricians (I'm a coward) are doing vaginal deliveries
of breech babies, but this isn't acceptable unless the baby is estimated
to be at least a pound less than a mother's previous largest baby, the
baby is a frank breech, and the maternal pelvic measurements are generous.
Any breech that is a first baby should still be born by C-section,
because it's easier to explain a possibly unnecessary C-section than to
explain a baby that was traumatized by the too large "after-coming" head.
There are many who warn that even successful vaginal deliveries of breech
babies result in what are called "soft" neurological signs that
is, not brain damage, but Attention Deficit Disorder, dyslexia, hyperactivity,
and the like.
Occasionally I'll encounter a baby that's in
a crazy position, like transverse (whole body sideways) or shoulder-first.
C-section is the safest way to address this
malpresentation; this is common sense when the unified vector forces of
labor don't push a head-first baby outward, but instead crunch a baby that's
not pointing straight down.
If you think the placenta can crowd out an
adequate space, imagine what an extra baby does to the locale! Twins
will compete for the most comfortable space, but usually there's a
membrane which will separate them and favor one to be lower. The big risk
here, though, is a breech baby that's first, compared to the head-first
second twin. In this positioning, the head of baby 1 (the breech), may
sit just above the head of baby 2 (the higher of the babies). When labor
ensues for a vaginal delivery, it's possible to have the horror of interlocking
heads. Needless to say, a breech/head-first presentation of twins necessitates
a C-section.
But head-first/head-first twins can deliver
vaginally, as can head-first/breech. Except, once again, when cowardice
rears it's common-sense head. There can be a considerable wait sometimes
for baby #2 to descend, and with this there's the possibility of a prolapsed
cord which could cut off oxygen to this twin. Because of this, although
not mandatory, some doctors do C-sections on all twins.
Delivery of a baby (or babies) requires a knowledge
of the baby's position. A baby's position is sometimes for a reason, but
often there's no explanation for alternatives to the most common head-first
("vertex"). With third and fourth generation antibiotics and advanced surgical
technique, the risk to the mother from a C-section
is now outweighed by the benefit to the baby when there's positioning that
would make vaginal delivery hazardous. In contrast
to the dangerous times of just a generation ago, we no longer need to seek
heroic vaginal deliveries for these babies. And even using this way out,
the C-section rate can still be kept low by waiting for proper descent
of the baby's head into the maternal pelvis before administration of an
epidural.
