06.02 Mechanisms of Labor

In this lesson I will explain how labor and the delivery occurs and your role in assisting the patient in a successful delivery.

The mechanisms of labor are known as the cardinal movements. These are the movements that the fetus does to find its way out. So first the fetus has to be engaged. This is the head in the pelvis engaged in and not moving back up. This can happen a few weeks before delivery and is also known as “lightening”. Now descent, so the fetus is moving further towards the “exit” and flexion of the head occurs. Flexion is that chin to chest to help the fetus move it’s way out. Descent is spoken in terms of the station that the fetus is in. This is discussed in the module on process of labor but basically you can see in this image that zero station means the fetus is at the ischial spines of the pelvis. As the baby gets closer to delivery it will be lower which is measured in centimeters and described as +1, +2 and so on. If the fetus is higher up above the ischial spines then it is -1,-2 and so on. The fetus will then have internal rotation. So it is going to rotate itself around then extend itself.

So after internal rotation we have extension. It will extend its neck so it is not chin to chest anymore to better get itself under those pelvis bones. The face is aligned with the maternal rectum and extends its head. This movement ends with the head delivering. Then there will be external rotation. So the head is delivered and it will rotate to realign its body. Sometimes the physician will help to do this. Last is expulsion. That fetus is going to expel the rest of its body out. In this image you can see the head is applied to the cervix and the cardinal movements start. The head is engaged and there is descent of the fetus. The fetus internal rotates and extends. External rotation can now occur to deliver or expel the rest of the body. There is also a great youtube video attached to this lesson that you can watch to visualize each movement.



For mechanisms of labor the patient needs to be in true labor. So let’s look at true labor versus false labor. True labor are contractions that are regular and can be timed. They are contractions that cause cervical change so dilation and effacement. Nothing stops them. False labor occurs because the uterus is a muscle and it contracts to prepare for childbirth. So it has to get the body ready. Sometimes false labor can feel like true labor. False labor are contractions that are not strong or regular. They make no cervical change. False labor can be stopped by hydrating and resting. Patients will also be told to walk to see if contractions are true labor. Walking will either cause them to get stronger and closer together because they are true labor but in false labor they will stop or not increase.

Now let’s look at the other items that occur prior to labor. Lightening is when the fetus drops, this just means the fetus descends further into the pelvis. When this happens two things occur. The patient can breath better because the fetus is lower and off the lungs. So that is a plus! But now it is lower and puts pressure on the bladder so the patient will have to void more. Vaginal discharge increases because of the cervix ripening and getting softer. There might be brown or blood tinged cervical mucus passing. This is pieces of the mucus plug. If you are a labor nurse then you will no doubt will have a patient at some point show up with a tupperware container and her mucus plug in it! They think this thing comes out and it means it is baby time. It can occur a few weeks prior to delivery though. Some woman won’t lose the plug as a whole. Some women will just have increased discharge and this is still the plug thinning out. The cervix is going to be softening and ripening possibly making some slight dilation and effacement. The patient might have a burst of energy known as nesting where the patient is quickly cleaning everything and getting ready for the baby. A fluctuation in hormones can cause a fluid shift and so weight loss might occur.

For delivery the bag of water must break. This can occur in several ways and different times. A PPROM means preterm premature rupture of membranes. This occurs prior to 37 weeks and the patient is at risk for infection. PROM is premature rupture of membranes. This occurs prior to labor. So she ruptures but is not in contracting. This could be a gush of fluid or a steady leak. Patients can either SROM, which is a spontaneous rupture of membranes at full term or AROM, which is an artificial rupture of membranes. This is done by the physician with an instrument to break the water. Infection is a risk for any rupture because that barrier is gone. PPROM patients are at the greatest risk because they are not in labor, which means they will be pregnant longer with no barrier.

Our management might involve rupturing the membranes or bag of water. This would be when the physician performs an AROM. When this occurs it gets rid of the buffer of the amniotic fluid in uterus. Fetal head will be able to drop and be on cervix and will stimulate uterine contractions and then labor. For a patient that comes in thinking that her water has broken then we may need to perform a Nitrazine test. This will determine if mother has urinated or ruptured membranes. Pregnant patients pee on themselves, it just happens so it is not an uncommon thing to have occur. The test is a strip of paper that is vagincally swabbed and it will turn blue if it is the amniotic fluid. The fluid is alkaline so it will turn blue in the presence of amniotic fluid.
The patient is going to need to be educated on true versus. false labor. In true labor the contractions can be timed regular, get stronger and closer together. and they do not stop with rest or activity. False labor is when contractions are not regular, do not get stronger or closer together, they stop with rest, hydration, and activity. They need to also know when to call the physician. SO for things like rupture of membranes, contractions 5 minutes apart, and bleeding.

Reproduction is reproduction has occurred and comfort to be provided during labor.
Ok so let’s look at our key points. The cardinal movements are engagement, descent and flexion, internal rotation, extension, restitution and external rotation, and expulsion. Labor can be true or false so we need to ask are they regular contractions? Is there cervical change? Do they go away or stay? And last our rupture of membranes. If it happens prior to 37 weeks it’s PPROM. PROM is rupture prior to labor. SROM is when the patient ruptures on her own at term and AROM is when the physician does it. It is artificial rupture.

Make sure you check out the resources attached to this lesson and look at each movement for the cardinal movements. Now, go out and be your best selves today. And, as always, happy nursing.