PHASES AND STAGES OF LABOR
Category: Special Populations
Next Unit: Fetal Circulation
18 minute read
Labor and delivery are delineated into Stages 1, 2, and 3.
- Stage 1 is a progression from latent phase to active phase, until complete dilation is accomplished.
- Stage 2 is from complete dilation to delivery.
- Stage 3 is from delivery until placental delivery.
This is from the time of active dilation of the cervix until complete dilation (usually 10 cm.).
It does not include "Braxton-Hicks" contractions, which are disorganized contractions that can occur anytime after 20 weeks gestation (halfway through the pregnancy).
- LATENT PHASE: Stage 1 begins when contractions become constant, although the time between them can vary during a beginning, or, "latent" phase. During the latent phase, although the contractions are constant, they are not really rhythmic.
The time between contractions is called the "refractory" period, and the refractory periods during the latent phase of labor can be from under a minute to as long as a half-hour. Latent phase of labor is often referred to as "false" labor because it does not actively dilate the cervix and it may spontaneously resolve without progressing into active labor. But this is not the best way to think of it.
- False labor comes and goes.
- Latent phase is a phase of actual labor, doesn't come and go, but progresses on to active labor.
- ACTIVE PHASE: The active phase of labor actively dilates the cervix by a process of progressively more frequent and strengthening contractions.
As opposed to latent phase contractions, these are organized into a net vector force downward, pushing the infant's presenting part (usually the head), as a dilating wedge against the cervix. As the cervix yields--as its fiborelastic circumference weakens--it begins to thin out and open, its circular structure said to dilate.
Latent Phase of Stage 1
Primigravidas (women experiencing their first pregnancy) have a cervix which has never been dilated. Alternatively, many multiparas (women who have experienced childbirth before) have a "used" cervix--one that has been stretched and then reformed, at least once--perhaps many times. Therefore, primigravidas often are undilated at term. Multiparas often are dilated to some extent at term, before labor, because of weakness in the cervix from previous delivery. This is why the active phase is defined as the active dilation of the cervix.
To illustrate, a woman is not in active labor if she is multiparous and has a cervical dilation of 3-4 cm which has been the same for a month. However, a woman that dilates from 3 cm to 4 cm in association with rhythmic contractions is in active labor.
The latent phase of labor will dilate the cervix form 0-3 cm, and it will begin a transition to an active phase at about 4 cm. This is when reflexes kick in to stimulate more contractions to cause more dilation--a vicious cycle of sorts. This is also a time when the discomfort of the contractions makes a big leap in discomfort.
Since severe pain can cause nausea and vomiting, nausea is often a reliable omen that the laboring woman has transitioned into active labor from the latent phase. If a woman is planning on having an epidural anesthetic, this transition time is usually when she insists on it (there is no understating how painful normal contractions of the uterus can be!).
The Active Phase of Stage 1
During the active phase, contractions are organized and very rhythmic, anywhere from every 2-4 minutes (measured from beginning of contraction to the beginning of the next) and lasting as long as 45-50 seconds. Backaches and the bloody show are common during this phase.
The backache is from the stretching of the ligaments that are attached to the cervix which is dilating and also the fetus pressing against the cervix with each contraction.
Bloody show is from the tearing of microscopic bridging blood vessels in the cervix with dilation.
HYPERTONIC CONTRACTIONS: Contractions coming more frequently than every 2 minutes are considered "hypertonic." This can risk fetal distress and placental abruption. The fetal distress is because the refractory periods between contractions are not long enough for the baby to recover from the stress of the contraction; also, the refractory period is when the baby gets its oxygenation, because circulation to the placenta is compromised during contractions.
HYPOTONIC CONTRACTIONS: Contractions that are enough to begin active phase but then space out to longer than every 3-5 minutes are considered hypotonic and can result in a secondary arrest of labor. This can happen with prolonged labor when the uterine muscle becomes exhausted.
This is the stage from complete cervical dilation to expulsion of the newborn.
Engagement: As the fetal head (or in breech, another presenting part) enters the pelvis, it is called "engagement." This usually happens during Stage 1 of labor, but can occur in multiparas even before labor begins.
Engagement begins the struggle to descend through the birth canal, the propulsive effect of contractions opposing the pelvic and vaginal tone in the progress toward delivery. At this point there are internal rotation of the fetal head to navigate the pelvis until the head is at the vaginal opening. When the infant's presenting part is so low that it compresses the rectum, a woman may state she has the urge to defecate, but this is false signalling, the rectum unable to discern between pressure from within (stool) versus outside (baby). When this occurs from pressure of the baby's head, delivery is imminent, and is usually followed by the urge to push.
Full cervical dilation (10 cm) is based on the assumption that it is the head that is the presenting (first delivering) part. In situations in which the presenting part is not a normally-sized fetal head (e.g., small in preterm babies), delivery can occur before the cervix reaches 10 cm.
If all goes normally, the head and then both shoulders will deliver. An attendant can assist with gentle traction, but it is really a spontaneous event. Once both shoulders are out, the rest follows quickly.
Spontaneous birth is a normal, natural process, but it can be impeded by fetal position changes. Fetal positioning changes include
- the descent through the birth canal,
- internal rotation,
- external rotation, and
In the field, you won't even be involved until step #7--Expulsion.
This is the time from fetal expulsion to placental expulsion.
There is a natural cleavage plane between the maternal uterine tissue and the fetal placental tissue, and the loss of the effects of the fetal circulation (via delivery) causes the placenta to shrink, crimping the area adjacent to the uterine wall; the natural cleavage plane thereby separates until complete detachment, at which time continued uterine contractions push the placenta out.