What are the theories of labor onset
Labour is the process by which a viable foetus i.e. at the end of 28 weeks or more is expelled or is going to be expelled from the uterus. Show Delivery means actual birth of the foetus. The following criteria should be present to call it normal labour:
Cause of Onset of Labour It is unknown but the following theories were postulated: Hormonal factors
Mechanical factors
CLINICAL PICTURE OF LABOUR Prodromal (pre-labour) stage The following clinical manifestations may occur in the last weeks of pregnancy.
These are differentiated from true labour pain as follow: True Labour PainFalse Labour PainRegular.Irregular.Increase progressively in frequency, duration and intensity.Do not.Pain is felt in the abdomen and radiating to the back.Pain is felt mainly in the abdomen.Progressive dilatation and effacement of the cervix.No effect on the cervix.Membranes are bulging during contractions.No bulging of the membranes.Not relieved by antispasmodics or sedatives.Can be relieved by antispasmodics and sedatives.Onset of Labour It is characterised by:
STAGES OF LABOUR Labour is divided into four stages:
First Stage Causes of cervical dilatation
Mechanism of cervical dilatation
Phases of cervical dilatation
The phase of maximum slope is the most detectable and the two other phases are of shorter duration and can be detected only by frequent vaginal examination. The normal rate of cervical dilatation in active phase is 1.2 cm/ hour in primigravidae and 1.5 cm/hour in multiparae. If the rate is < 1cm / hour it is considered prolonged. Second Stage Delivery of the head
Delivery of the shoulder and body The anterior shoulder hinges below the symphysis pubis and with continuous descent the posterior shoulder is delivered first by lateral flexion of the spines followed by anterior shoulder then the body. Third Stage After delivery of the foetus, the uterus continues to contract and retract. As the placenta is inelastic, it starts to separate through the spongiosa layer by one of the following mechanisms: Schultze’s mechanism (80%)
Duncan’s mechanism (20%)
The 3rd stage is composed of 3 phases:
PHYSIOLOGICAL EFFECTS OF LABOUR On the Mother
On the Foetus Moulding The physiological gradual overlapping of the vault bones as the skull is compressed during its passage in the birth canal. One parietal bone overlaps the other and both overlap the occipital and frontal bones so fontanelles are no more detectable. It is of a good value in reducing the skull diameters but severe and / or rapid moulding is dangerous as it may cause intracranial haemorrhage. What are the theories explaining the onset of labor?Functional integrity of the fetal brain , pituitary and adrenal glands, kidneys, and membranes seems to be an important component of the organ communication theory as a cause of labor onset. This explanation does recognize the fetus 's production of cortisol, which is believed to stimulate the onset of labor.
What are the 5 theories that will initiate labor?Oestrogen theory: During pregnancy, most of the oestrogens are present in a binding form. ... . Progesterone withdrawal theory: Before labour, there is a drop in progesterone synthesis leading to predominance of the excitatory action of oestrogens.. Prostaglandins theory: ... . Oxytocin theory: ... . Foetal cortisol theory:. What is the onset of labor?Labor usually starts two weeks before or after the estimated date of delivery. However, the exact trigger for the onset of labor is unknown. While the signs of labor may vary, the most common are contractions, rupture of the amniotic sac (“breaking your water”) and bloody show.
Which are the factors that affect the onset of labor?Factors Affecting Labor. At least five factors affect the process of labor and birth. These are easily remembered as the five Ps: passenger (fetus and placenta), passageway (birth canal), powers (contractions), position of the mother, and psychologic response.
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