Now let's discuss the first stage of labor.
So in review of all of our stages of labor, let's remember
that Stage 1 starts from onset of labor
until 10 centimeters dilated.
Stage 2 is 10 centimeters dilated until the delivery
of the infant.
And Stage 3 starts with the delivery of the infant
and ends with delivery of the placenta.
So in Stage 1 we have contractions that are causing
cervical change and they are also causing the fetus to
descend in the pelvis.
We can further divide Stage 1 into latent labor which is onset
of contractions until 4 centimeters dilated.
And into the active phase.
This is from 4 centimeters dilated
to 10 centimeters dilated.
Now let's consider normal.
For our primiparous first time moms, the latent labor can last
to 6 to 11 hours.
For multiparous 4 to 8 hours.
In the active phase we expect the cervix to change
1.2 centimeters per hour for out first time moms.
And 1.5 centimeters per hour for our multiparous moms.
So we have an abnormal first stage labor.
What causes that?
Well, when we think of the 3 P's.
Power, Passenger and Pelvis.
With power we're talking about the strength of contractions.
Now how do we measure the strength of the contractions.
Typically in labor our moms are going to have a monitor on that
tells us them externally how often they are contracting.
If we want to know how strong the contractions are,
we place an intrauterine pressure catheter
that measures something called "The Montevideo Units."
The Montevideo units are a measurement
that are taken over 10 minute strip looking at all
of the contractions and measuring the area
under the curb.
We expect it to be 180 to 220 Montevideo units
to say the contractions are adequate.
If those contractions are not adequate, we're going to start
a medication called Pitocin.
This is a synthetic form of oxytocin and this makes
the contractions stronger.
Now our next P is passenger.
So what can go wrong with our passenger to make
the first stage of labor abnormal.
Well we could have malrepresentation
of our passenger such as a breech presentation,
a face presentation or brow presentation.
That will prevent the passenger from coming down the pelvis.
Or the passenger could be having fetal heart rate issues.
Now, our next P is the pelvis.
Now there is no way to determine what type of pelvis
a patient has prior to labor.
But just to note, there are 4 different types of pelvises.
And depending on the type of pelvis that can ease
the delivery or it can make the delivery more difficult.
So the gynecoid pelvis is one that allows the head to always
rotate to also put anterior making vaginal delivery
pretty easy.
Anthropoid pelvis more common in African American women cause
the fetal head to rotate to the occipit posterior position.
While they can still have a vaginal delivery,
sometimes that can be a little difficult.
And sometimes it requires an operative vaginal delivery to
get those last little maneuvers to have the fetal head go
underneath the pubic symphysis.
The platypeloid pelvis will cause the fetal head to be
in a transverse position.
If you remember from our previous lecture,
we need that fetal head to occipit anterior or occipit posterior
so that only 9 and half centimeters of the fetal vertex
is trying to pass through the pelvis.
Remember that the fetal pelvis is largest at 10 centimeters
at it's largest point.
A transverse presentation is not going to be able to be pass
through the pelvis.
And an android pelvis is more like a guy's pelvis
and that is heart shaped.
And in this type of presentation the fetal head has difficulty
even engaging.