Physiological Changes during First Stage of Labour

Subject: Midwifery II (Theory)

Overview

Muscles contract and retract during the early stage of labor. Where the thick upper segment meets the thinner lower segment, a ridge known as the retraction or Bandle's ring forms. Effacement of the cervix refers to the gradual thinning and shortening of the cervix. The top segment's retracted muscle fibers apply upward pressure, pulling on the cervix's weaker margin to spur os development. The next modification is the introduction of a performance during the early phases of labor. The blood-tinged mucoid discharge is seen just before and after labor starts. Lastly, a water bag has to be built. The decidua, which borders the uterine cavity other than the internal os, is only tangentially connected to the membranes (amnion and chorion). Since the skull is round, the girdle may touch the lower segment wall when the head is presented in a vertex position. The amniotic sac therefore divides in two.

First Stage of Labour

  • Consistent uterine contractions are the first step, while full cervical dilatation at 10 cm is the last.
  • The process comprises two phases: the latent and the active.
  • During the latent period, the cervix is shortened and loosened by mild, erratic uterine contractions.
  • After some time has passed, the contractions get stronger and more regular in rhythm.
  • In most cases, rapid cervical dilatation and the fall of the presenting fetal part signal the beginning of the active phase, which begins at around 3–4 cm of cervical dilation.

Physiological Changes

  • Uterine muscle, contraction, and retraction:
    • Uterine contractions, which occur without the woman's active participation, are regulated by the nervous system and the hormones. Rhythmic regularity characterizes their occurrence, with initial intervals of roughly 15 minutes decreasing to a few minutes by the conclusion of the first stage.
       
  • Fundal dominance:
    • The fundal area near the cornua is the starting point for each contraction, which then moves downhill and throughout the abdomen, with the upper section being the strongest and lasting the longest. Fundus and midzone stability throughout the contraction.
       
  • Intensity
  • Degree of uterine systole
  • Probably influenced by the hormone
  • Sometimes diminished pain due to lack of stretching effect
     
  • Polarity:
    • The term "polarity" is used to describe the state of harmony between the uterine muscles at opposite poles. These two poles function in tandem during uterine contractions. The fetus is released when the top pole contracts slightly and then dilates. If the polarity is disorganized, the work cannot advance.
       
  • Retraction: 
    • When the contraction in the uterine muscle is incomplete, a process known as retraction occurs. During this phase, the muscular fibers retain some of the contraction rather than entirely releasing. The uterine cavity decreases in size and the top part of the uterus shorten and thickens, both of which contribute to the gradual rejection of the embryo.
       
  • Development of retraction ring
    • The ridge that separates the thicker upper segment from the thinner lower section is called the retraction or Bandle's ring. Normal labor includes the presence of this till it is no longer visible above the symphysis pubis. Because the fetus is gradually expelled through the dilating cervix, this is not noticeable during natural labor and delivery. However, in obstructed labor, the lower segment must elongate to accommodate the fetus as it is forced down through the narrowed upper sections. In such a situation, the retraction ring would be seen across the belly, somewhat obliquely above the symphysis pubis. The uterus may burst as a result. When the ring is not visible, the retraction ring is utilized, however when it becomes visible, Bandl's ring is utilized.
       
  • Taking up of the cervix
    • It is also known as cervical effacement. This condition involves the cervical process becoming thinner and shorter. After some time, the cervix will become effaced. The muscle fibers that surround the internal os are drawn upward as the top segment is retracted. Shortening and effacing of the cervix precedes complete dilatation, and the taking up of the cervix marks the end of the first stage of labor.
       
  • Dilatation of the cervix
    • The outer os expands from a circular opening. The top segment's retracted muscle fibers apply upward pressure, pulling on the cervix's weaker margin to spur os development. Having the baby's head flexed and close to the cervix will facilitate dilatation. In primigravidae women, the external os may be closed at the beginning of labor or may admit the tip of one finger, and it does not enlarge until the cervix is taken up. Multiparous women often have one finger admitted via the external os prior to labor starting, and both the external and internal os dilate at the same time as the cervix is being taken up.
       
  • Show
    • Even in the early stages of labor, there is already a performance going on. The blood-tinged mucoid discharge is seen just before and after labor starts. When a woman is pregnant, the cervical plug, also called an operculum, is formed by a thick, resilient fluid called mucus. The cervix dilates and capillaries in the decidua vera, where the chorion has been detached, and ruptures, releasing the blood.
       
  • Formation of the bag of water
    • The decidua, which borders the uterine cavity other than the internal os, is only tangentially connected to the membranes (amnion and chorion). Due to the spherical nature of the head, the wall of the lower segment may make contact with the girdle of the head when in vertex presentation. The amniotic sac, therefore, divides in two. The fetus and most of the liquid known as hind water are located above the girdle of contact, while just a little amount of forewater is located below it. At the onset of labor, the membranes that had been attached to the lower uterine segment separate; then, when intrauterine pressure rises as a result of contractions, the membranes herniate into the cervical canal. Since the well-flexed head acts like a ball valve, the applied force from uterine contractions is not transmitted accurately, causing the bag of membranes to bulge out and stay intact until the cervix is nearly fully dilated. Increasing cervical dilatation requires pushing on a bag of membranes. Rupture of the membranes is commonly utilized in clinical practice for both induction and augmentation of labor.

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Things to remember
  • Muscles contract and retract during the early stage of labor.
  • Where the thick upper segment meets the thinner lower segment, a ridge known as the retraction or Bandle's ring forms.
  • Normal labor includes the presence of this till it is no longer visible above the symphysis pubis.
  • When the cervix is retracted, a condition known as cervical effacement develops.
  • This condition involves the cervical process becoming thinner and shorter.
  • The outer os expands from a circular opening.
  • The retracted muscle fibers of the upper segment provide upward traction, pulling on the cervix's margin, assisting in the dilation of the cervix.
  • The blood-tinged mucoid discharge is seen just before and after labor starts.
  • Lastly, a water bag has to be built. The decidua, which borders the uterine cavity other than the internal os, is only tangentially connected to the membranes (amnion and chorion).
  • Since the skull is round, the girdle may touch the lower segment wall when the head is presented in a vertex position.
  • The amniotic sac therefore divides in two.
Questions and Answers

Physiological changes are

  • Uterine muscle contraction and retraction.
  • Involuntary uterine contractions are regulated by the endocrine system and the neurological system. The intervals between them gradually get shorter, going from roughly 15 minutes at the start of the first stage to two or three minutes at the end. They typically occur rhythmically.
  • Fundal dominance: Every contraction begins in the area close to a cornua and spreads downward and across, with the upper region experiencing stronger contractions that last longer. Throughout the contraction, the fundus and mid-zone are hard.
  • Intensity.
  • Uterine systole level.
  • Likely affected by hormone.
  • In certain cases, reduced discomfort results from a lack of stretching effect.
  • Polarity: The neuromuscular balance that exists between the two poles of the uterus throughout labor is referred to as polarity. Each time the uterus contracts, these two poles work in unison. The top pole gently contracts before expanding to allow the fetus to be expelled. The labor does not advance if the polarity is disordered.
  • Retraction: Retraction is a unique ability of the uterine muscle in which the contraction is partially retained by the muscle fibers rather than completely dissipating. Retraction aids in the fetus's progressive expulsion, and the uterus's upper segment gets shorter and thicker while losing some of its cavity.
  • Development of Retraction Ring

The retraction, often referred to as Bandle's ring, is the ridge that forms the lower border of the thick upper segment where it meets the thinner lower segment. It occurs during every labor and is quite normal up until the point where it isn't noticeable above the symphysis pubis. Because the fetus is gradually being ejected via the dilating cervix, it is not visible during a typical labor. However, in obstructed labor, where the fetus is forced out of the shorter upper segments because it cannot descend to pass through the cervix, the bottom segment must extend to make room for it. In such cases, retraction ring would be visible transversely or slightly obliquely across the abdomen, above the symphysis pubis. It may cause rupture of the uterus. Retraction ring is termed in a case of invisible and Bandl's ring when it becomes visible.

  • Taking up of Cervix

Additionally called cervical effacement. The cervix gets thinned and shortened throughout this procedure. The cervix progressively effaces, taking on the form of a funnel. The retracted upper segment pulls up the muscular fibers that surround the internal os. The cervix gradually shortens and effaces; when the cervix is fully dilated, the first stage of labor has ended and the cervix is taken up.

  • Dilatation of the Cervix

The external os begins to enlarge from a circular opening. Its aided by upward traction, exerted by the retracted muscle fibers in the upper segment exerts pull on the margin of the weakened area- the cervix and makes the os enlarge. The well-flexed head will which closely applied to the cervix, aid dilatation.

In the primigravidae woman, the external os may be closed at the beginning of labour or it may admit the tip of one finger and does not dilate until the cervix has been taken up, but the internal os dilates during the process of taking up of the cervix. In the multiparous woman, the external os usually admits one finger prior to the onset of labour and dilatation of the external and internal os proceeds simultaneously with taking up of the cervix.

  • Show

There is a presence of show during the early stage of labor. The blood-stained mucoid discharge that is visible just before or shortly after labor has begun serves as evidence. During pregnancy, the mucous, a dense, tenacious substance, formed the operculum, the cervical plug. The blood is produced by the dilating cervix and ruptured capillaries in the decidua vera, where the chorion has separated.

  • Formation of the bag of water

The decidua, which lines the uterine cavity with the exception of the internal os, is loosely linked to the membranes (amnion and chorion). The girdle of the skull, which is spherical, may be felt in vertex presentation together with the lower segment wall. As a result, the amniotic cavity is split into two sections. The majority of the fetus's liquid, known as hind water, is located above the girdle of contact, while fore water is mostly present below it. When labor begins, the membranes affixed to the lower uterine segment become detached, and as the pressure inside the uterus increases during contractions, the membranes herniate through the cervical canal. The bag of membranes bulges out and stays intact until the cervix is almost fully dilated because the force of uterine contractions cannot be transmitted squarely due to the well-flexed head's ball-valve-like action. For the cervix to gradually enlarge, pressure must be applied to a membrane bag. In clinical practice, the rupture of the membranes is also used for labor induction, labor augmentation, and labor induction.

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