Labor and its physiology 2022-2023 4th year

FACTORS THAT INFLUENCE PROGRESS OF LABOUR 3ps
Power
Passage
passenger<br>

Causes of Onset of Labor: A. Hormonal factors
1) Estrogen theory: During pregnancy, most of the estrogens are present in a binding form. During the last trimester, more free estrogen appears increasing the excitability of the myometrium and prostaglandins synthesis
2) Progesterone withdrawal theory: Before labour, there is a drop in progesterone synthesis leading to predominance of the excitatory action of estrogen
3) Prostaglandins theory: Prostaglandins E2 and F2α are powerful stimulators of uterine muscle activity. PGF2α was found to be increased in maternal and fetal blood as well as the amniotic fluid late in pregnancy and during labour.<br>

4) Oxytocin theory: Although oxytocin is a powerful stimulator of uterine contraction, its natural role in onset of labour is doubtful. The secretion of oxytocinase enzyme from the placenta is decreased near term due to placental ischemia leading to predominance of oxytocin’s action.


5) Fetal cortical theory: Increased cortisol production from the fetal adrenal gland before labour may influence its onset by increasing estrogen production from the placenta<br>

B.Mechanical factors
1) Uterine distension theory
2) Stretch of the lower uterine segment by the presenting part near term triggered the synthesis of prostaglandin
C. Neurological factor:
1. Both α and β adrenergic receptors are present in the myometrium; estrogen causing the α receptors and progesterone the β receptors to function predominantly.
2. The contractile response is initiated through the α receptors of the post ganglionic nerve fibers in and around the cervix and the lower part of the uterus<br>

SYMPTOMS AND SIGNS OF LABOUR Before labour begins, women usually notice one or more premonitory, or warnings, signs that labour is about to begin.
They are:
1.Painful regular uterine contractions – as evidence by contraction at least one in ten minutes
2.Show – as evidence by mucus mixed with blood
3.Rupture of membranes – as evidence by leaking liquor
4.Progressive shortening and dilatation of the cervix<br>

The stages of labor Labour can be divided into four stages:
First stage This stage starts from the onset of labour to full dilatation of the cervix (10 cm). Its average duration is 12 hours in primigravida and 6 hours in multigravida
The first stage of labour can be divided into two phases:
The ‘latent phase’ is the time between the onset of labour and 3–4 cm dilatation. During this time, the cervix becomes ‘fully effaced.
Effacement is a process by which the cervix shortens in length as it becomes included into the lower segment of the uterus. The process of effacement may begin during the weeks preceding the onset of labour, but will be complete by the end of the latent phase. The cervical os cannot usually begin to dilate until effacement is complete. Effacement and dilatation should be thought of as consecutive events in the nulliparous woman, but may occur simultaneously in the multiparous woman.<br>

Dilatation is expressed in centimeters between 0 and 10. The duration of the latent phase is variable, However, it usually lasts between 3 and 8 hours, being shorter in multiparous women


The second phase of the first stage of labour is called the ‘active phase’ and describes the time between the end of the latent phase (3–4 cm dilatation) and full dilatation (10 cm). It is also variable in length, usually lasting between 2 and 6 hours. Again, it is usually shorter in multiparous women. Cervical dilatation during the active phase usually occurs at 1 cm/hour or more in a normal labour<br>

Physiological changes that occur in first stage Uterine action:
♦fundal dominance:
Contractions start in the fundus and spreads across and downward,usualluly its lasts longest and its more intense in the fundus, but the peak reached simultansly over the whole uterus and fades from all parts together .
polarity
Its term describe the neuromuscular harmony between two pols or segments of uterus throughout labour ,during contraction the upper pole(upper uterine segment )contract strongly and retract to expel the fetus the lower pole(lower uterine segment) contract slightly and dilates to allow expulsion to occur if polarity disorganized the progress of labour is inhibited.<br>

contraction and retraction Contraction
During contraction, uterus becomes hard and somewhat pushed anteriorly to make the long axis of the uterus in the line with that of pelvic axis. Simultaneously, the patient experiences pain which is situated more on the hypogastric region, often radiating to the thighs.
Probable cause of pain are -
- Myometrial hypoxia during contractions.
- Stretching of the peritoneum over the fundus.
- Stretching of the cervix during dilatation.
- Compression of the nerve ganglion.
The pain of uterine contractions is distributed along the cutaneous nerve
distribution of T10 to L1.<br>

Intensity - The intensity of uterine contractions describes the degree of uterine systole. The intensity gradually increases with advancement of labour until it becomes maximum in the second stage during delivery of the baby. Intrauterine pressure is raised to 40-50 mm Hg during first stage and about 100-120 mm Hg in the second stage of labour during contractions.

Duration - In the first stage, the contractions last for about 30 second initially but gradually increases in duration with the progress of labour.Thus in the second stage,the contractions last longer than in the first stage.<br>

Frequency - In the early stage of labour, the contractions come at intervals of 10-15 minutes. The intervals gradually shorten with advancement of labour until in the second stage, when it comes every two or three minutes.

Retraction
is a phenomenon of the uterus in labour in which the muscle fibers are permanently shortened
The effect of retraction on normal labour are -
- Essential property in the formation of lower uterine segment and dilatation and effacement up of the cervix.
- To maintain the descend of the presenting part made by the uterine contractions and to help in ultimate expulsion of the fetus.
- To reduce the surface area of the uterus favoring separation of placenta.
- Effective haemostasias after the separation of the placenta<br>

Formation of upper and lower uterine segments The upper uterine segment, having been formed from the body of the fundus, is mainly concerned with contraction and retraction; it is thick and muscular.
The lower uterine segment is formed of the isthmus and the cervix, and is about 8-10 cm in length. The lower segment is prepared for distention and dilatation.
The muscle content reduces from the fundus to the cervix, where it is thinner.
When the labour begins, the retracted longitudinal fibres in the upper segment pull on the lower segment causing it to stretch; this is aided by the descending presenting part.<br>

Cervical effacement

Effacement refers to the inclusion of the cervical canal into the lower uterine segment. It takes place from above downward; that is, the muscle fibres surrounding the internal os are drawn upwards by the retracted upper segment and the cervix merges into the lower uterine segment
Cervical dilatation
Dilatation of cervix is the process of opening of the cervix from a tightly closed aperture to an opening large enough to permit the passage of the fetal head. Dilatation is measured in centimeters and full dilatation at term equates to about 10 cm<br>

Show
As a result of the dilatation of the cervix, d the cervical plug is lost. The which is a blood stained mucoid discharge a few hours before, or within a few hours after, labour starts. The blood comes from the ruptured capillaries in the parietal decidua where the chorion has become detached from the dilating cervix.
Formation of fore water
As the lower uterine segment forms and stretches, the chorion becomes detached from it and the increased intrauterine pressure causes its loosened part of the sac of fluid to bulge downwards into the internal os<br>

Rupture of membrane
The optimal physiological time for the membranes to rupture spontaneously is at the end of the first stage of labour after the cervix becomes fully dilated and no longer supports the bag of forewater
Fetal Axis Pressure
During each contraction the uterus rises forward and the force of the fundal contraction is transmitted to the upper pole of the fetus down the long axis of the fetus and applied by the presenting part to the cervix<br>

Second stage : This describes the time from full dilatation of the cervix to delivery of the fetus or fetuses. The second stage of labour may also be subdivided into two phases:
The passive phase:
Its start from full dilatation upto the descent of the presenting part to the pelvic floor. There is no maternal urge to push and the fetal head is still relatively high in the pelvis<br>

Active second stage There is a maternal urge to push because the fetal head is low (often visible), causing a reflex need to ‘bear down’. In a normal labour, second stage is often diagnosed at this point. If a, the active second stage is said to begin when she starts making voluntary active efforts. Conventionally, a normal active second stage should last no longer than 2 hours in a primiparous woman and 1 hour in those who have delivered vaginally before, but there is evidence that a second stage of labour lasting more than 3 hours is associated with increased maternal and fetal morbidity. Use of epidural anaesthesia may influence the length and the management of the second stage of labour<br>

Physiology of second stage of labour Fetal axis pressure increases flexion of the head, which results in smaller presenting diameters, more rapid progress and less trauma to both mother and fetus.
Uterine action: Contractions become stronger and longer ,The contraction becomes expulsive as the fetus descends further into the vagina. Pressure from the presenting part stimulates nerve receptors in the pelvic floor and the woman experiences the need to push.
The mother‘s response is to employ her secondary powers of expulsion by contracting her abdominal muscles and diaphragm<br>

Soft tissue displacement
As the hard fetal head descends, the soft tissues of the pelvis becomes displaced.Anteriorly-Bladder Posteriorly- Rectum The levator ani muscles and Perineal body
The fetal head becomes visible at the vulva, advancing each contraction and receding between contractions until crowning takes place. The head is then born. The shoulders and body follow with next contraction<br>

Third stage : This stage begins immediately after delivery of the fetus and involves the separation and expulsion of the placenta and membranes, involving the separation, descent and expulsion of placenta and membranes and control of hemorrhage from the placenta site.The third stage usually lasts between 5 and 15 minutes.<br>

There is a signs of separation of placenta preceding any trial to delivery of it:
1.Gush of bleeding from site of separation of placental bed.
2.Increased the length of cord.
3.Uterus become round globular due to decreasing the size of uterus and starting of contractions.
4.Placenta in vagina on PV examination<br>

Physiology of third stage of labour As the neonate is born, the uterus spontaneously contracts around its diminishing contents. The uterine fundus now lies just below the level of the umbilicus. Thus, by the beginning of the third stage, the placental site has already diminished in area by about 75%.As this occurs the placenta becomes compressed and the blood in the intervillous spaces is forced back into the spongy layer of the decidua basalis.<br>

Fourth stage a postpartum period of about 4 hours after the third stage, or delivery of the placenta. Some complications, especially hemorrhage, occur at this time, necessitating careful observation of the mother
a.Observation for the patient particularly atony of the uterus and vaginal bleeding<br>