Summary of Stages of labor
Transcript for Stages of labor
Stages of labor
Labor, also called parturition, describes the hard work of delivering a baby!
It specifically refers to the process that starts with uterine contractions that cause cervical changes, which allow the fetus to be delivered vaginally, and ends with delivery of the placenta.
Labor typically begins at some point when the fetus is considered term—between 37 and 42 weeks’ gestation.
In the third trimester, before labor starts, a woman might have a plug of mucus and blood fall out of the opening to the cervix, sometimes called bloody show.
Other times the amniotic sac might rupture, sometimes called water breaking.
Either of these can trigger the onset of labor and so-called true labor contractions.
These guys have to be distinguished from the milder and ineffective false labor contractions, also called Braxton Hicks contractions (or sometimes called practice contractions).
Once they start, true labor contractions progress in frequency, duration, and intensity, and they can feel like waves that build up to a peak intensity and then gradually decrease.
The contractions pull on the thick tissues of the cervix, causing it to efface,or get thinner, and also dilate, or open up, so then the fetus can leave the uterus and enter the world.
From the moment true contractions begin to the baby’s delivery usually takes about 12 to 18 hours for a first-time pregnancy, and about half that time for subsequent pregnancies. Although, as any mother knows, this time can vary a lot!
Even though labor is a continuous process, it can be broken down into three stages.
Additionally, the first stage is subdivided into three phases.
The first phase is the early phase or latent phase, and usually lasts 8–12 hours with initially irregular contractions that can vary in frequency and duration, occuring every 5–30 minutes and generally lasting for a shorter period of time than the contractions of active labor.
During latent labor, the cervix dilates from 0 cm to about 4–5 cm and also becomes more effaced.
The active phase of the first stage usually lasts 3–5 hours with regular contractions that happen every 3–5 minutes, and which generally last longer, usually a minute or more.
During this phase of labor, the cervix dilates to approximately 7 cm and continues to thin out, generally becoming at least 80% effaced by this point.
Finally, at the end of the first stage of labor, there’s the transition phase, which usually lasts 30 minutes to 2 hours with very intense contractions that happen with only 30 seconds to 2 minutes of rest in between and lasting 60-90 seconds each.
This is the most intense phase, but it’s also the shortest, and causes the cervix to fully dilate from 7 cm to 10 cm with 100% effacement.
The amniotic sac may rupture at any point during these phases.
Now that the cervix is fully dilated, the woman enters the second stage of labor, which can be thought of as the pushing stage.
During this stage, the critical thing is for the baby and, in particular, the baby’s head, to navigate through the maternal pelvis, and this depends on the three Ps—power, passenger, and passage.
Power refers to forceful uterine contractions and maternal pushing effort; passenger refers to the fetus; and passage refers to the route that the fetus has to travel through the bony pelvis.
In fact, the relationship between the size of the baby’s head and the size and shape of the bony pelvis is so critical that human babies have evolved with unfused skulls, just so their head can be as large as possible prior to birth and still successfully and safely make that passage through the pelvis into the world.
Now there are a few factors that determine how easy this process is for the fetus… and for the mother.
First is fetal size and, most critically, the size of the fetal head.
Another important factor is fetal attitude, which refers to the way that the fetal body is flexed, not its personality.
When labor starts, the fetus is normally fully flexed, which means chin is on the chest, and they have a rounded back with flexed arms and legs.