Thus, fetal position within the uterine cavity should be determined at the onset of labor Fetal Lie The relation of the fetal long axis to that of the mother is termed fetal lie and is either longitudinal or transverse.
The musculature of the pregnant Mechanism of labor is arranged in three strata: An external hood-like layer which arches over the fundus and extends into the various ligaments.
An internal layer consisting of sphincter-like fibers around the orifices of the tubes and the internal os. Lying between the two, a dense network of muscle fibers perforated in all directions by blood vessels.
The main portion of the uterine wall is formed by this middle layer which consists of an interlacing network of muscle fibers between which extend the blood vessels. As the result of such an arrangement, when the cells contract after delivery, they constrict the vessels and thus act a "living ligatures.
It has been demonstrated that the uterus has pacemakers to produce the rhythmic coordinated contractions of labor.
These pacemaker sites are found near the uterotubal junctions, although the pacemaker cells do not differ Mechanism of labor from the surrounding myocytes as they do in cardiac muscle. The interval between contractions diminishes gradually from approximately ten minutes in early labor to as little as two minutes near the end of labor.
In the normal process there is a progressive increment in the strength of contractions form approximately 20 mm of mercury at the onset of labor to 50 to 80 mm late in labor. The effect of uterine contractions of this frequency and intensity is twofold on the uterine cervix.
First effacement consisting of thinning of the cervix with a shortening of the endocervical canal, is produced. Secondly, cervical dilation concurs, initially slowly as it accompanies the process of effacement of the cervix, and then more rapidly as cervical effacement has been accomplished see Figure 1.
Progressive contractile activity of the uterus has been demonstrated throughout pregnancy. Most of these contractions are imperceptible to the pregnant individual, but toward the end of pregnancy they may achieve on a sporadic basis strength equivalent to those of early labor. False labor, Braxton-Hicks contractions, and pre-labor contractions are terms that have been applied to this uterine activity.
The latter term is probably the most appropriate, and it is this uterine activity which accomplishes a significant degree of effacement and even some dilatation in the days or weeks prior to the onset of recognizable labor. Descent of the presenting part of the fetus into the birth canal, particularly in a first pregnancy, is another result of pre-labor.
The Mechanism of Normal Labor The definition or clinical diagnosis of labor is a retrospective one. There is no laboratory test that gives a "labor titer" or an x-ray procedure that can define the difference between the laboring and non-laboring patient. Realizing these limitations, the patient is diagnosed as being in labor when a combination of conditions exist.
Perhaps a good working definition may be stated as follows: When in the presence of perceived uterine contractions, there is progressive cervical dilation and descent of the presenting part which leads to the eventual expulsion of the products of conception, the patient is in labor.
The "mechanism of labor" refers to the sequencing of events related to posturing and positioning that allows the baby to find the "easiest way out. For a normal mechanism of labor to occur, both the fetal and maternal factors must be harmonious. An understanding of these factors is essential for the obstetrician to appropriately intervene if the mechanism deviates from the normal.
The following definitions must be mastered to be able to discuss and understand the mechanism of labor: This refers to the posturing of the joints and relation of fetal parts to one another.
The normal fetal attitude when labor begins is with all joints in flexion. This refers to the longitudinal axis of the fetus in relation to the mother's longitudinal axis; i.
This describes that part on the fetus lying over the inlet of the pelvis or at the cervical os.
Point of Reference or Direction. This is an arbitrary point on the presenting part used to orient it to the maternal pelvis [usually occiput, mentum chin or sacrum].
This describes the relation of the point of reference to one of the eight octanes of the pelvic inlet e. This occurs when the biparietal diameter is at or below the inlet of the true pelvis. This references the presenting part to the level of the ischial spines measured in plus or minus centimeters.
The single most important determinant to the mechanism of labor is probably pelvic configuration.Sep 05, · Describing the mechanism of labour is a common topic for OSCEs and MCQs.
Although on the surface it can appear complicated, breaking the process down into individual steps makes it much easier to understand.5/5(3). The mechanism of labor in all these presentations is usually similar. The positional changes in the presenting part required to naviga te the pelvic canal constitute the mechanisms of labor.
The cardinal movements of labor are engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion (Fig. ). During labor. To understand the mechanism of labor for a cephalic presentation.
To understand the meaning of the following germs: Presentation, position, lie, station, effacement, dilatation. To understand the phases and stages of labor.
The incidence of face presentation has been quoted as % of all deliveries. 6 In cases of face presentation, a vaginal delivery can be accomplished most frequently with a mentum anterior position, but the mentum posterior position will impede the fifth cardinal movement of labor (extension).
Mechanism of labour is the series of passive movements of the fetus during its passage through the maternal pelvis during labour. Principles of Mechanism of Labour 1. Oct 11, · Demonstration of the mechanism of normal labor with a model.
Useful for OSCEs. Please note that this focuses mainly on passive fetal movements during labour and it is likely that more knowledge will be needed for an OSCE station. 1. Descent a.