Labour
Labour is described as the process whereby the foetus, placenta and membranes are expelled through the birth canal after 28 weeks of gestation.
Labour, can be either normal or abnormal.
Normal labour has several important characteristics, which you should always remember.
These are:
Duration – completed within 18 hours
- Occurs at term between 38 and 40 weeks
- Is spontaneous
- The foetus presents by the vertex
- Has no complications to either mother or baby
- The newborn child requires minimal or no
The Onset of Labour
- A midwife should ensure women have sufficient information to assist them to recognize the onset of true labour.
- A pregnant woman would be best placed to diagnose the onset of labour herself.
- Some young women, especially the primigravidae (those pregnant for the first time), may fail to recognize true labour.
- It is important that you help them differentiate between false and true labour signs.
- The contractions of true labour are regular and intense.
- In false labour, the contractions are sporadic (Braxton-Hickscontractions).
- False contractions occur during the last weeks of pregnancy.
Signs and symptoms that gives evidence that the mother is in labour:
- Contractions of the uterus, which are increasingly strong, painful and regular.
- The cervix is taken up into the lower uterine segment causing dilatation of the cervix.
- There is a mucoid blood stained discharge, which is called show.
- Sometimes there is rupture of membranes with drainage of liquor amnii (amniotic fluid).
- The causes that trigger the onset of labour are not known.
- However, many theories have been offered which indicate that both hormonal and mechanical factors play a big part.
Hormonal Factors
It is believed that close to term progesterone levels in the body fall, while at the same time levels of oestrogen (which is responsible for sensitizing the uterine muscles) rise.
The fall in progesterone levels is important because it has effect on muscle contractions.
The rise in oestrogen levels meanwhile triggers the release of oxytocin, which causes uterine contractions.
The foetal hypothalamus is believed to produce releasing factors, which stimulate the anterior pituitary gland to produce adrenocorticotrophichormone (ACTH).
Mechanical Factors
Uterine activity can also result from the mechanical stimulation of the uterus and cervix.
This may be due to over stretching, as in the case of multiple pregnancy and polyhydromnios, or pressure from the presenting part, when it is well applied to the cervix.
It appears that there is a combination of hormonal (from both mother and foetus) and mechanical factors that set labour in motion.
Pre-Labour or Premonitory Signs of Labour
This is the period two to three weeks prior to the onset of labour when a number of changes take place.
Lightening
Two to three weeks before labour, the lower uterine segment expands allowing the foetalhead to sink deep.
The descent of the head and the body of the baby gives space to the lungs, heart and stomach, which enables these organs to function easily.
The symphysis pubis widens and the pelvic floor softens and becomes more relaxed, allowing further descent of the uterus into the pelvis.
Frequency of Micturition
The descent of the foetal head increases pressure within the pelvis.
This limits the capacity of the bladder, which can cause irritation.
The laxity of the pelvic floor muscles gives rise to poor sphincter control causing a degree of stress incontinence.
This pressure results in the congestion of circulation to the lower limbs.
Additionally the relaxation of the pelvic joint may give rise to backache.
Taking up of Cervix
The cervix is taken up gradually and merges into the lower uterine segment. Shortening of cervix is looked for when labour needs to be induced.
Contractions
The contractions of the uterus are coordinated by two pacemakers in the region of the cornua.
These are located where the fallopian tubes join the uterine body.
The muscle contractions start at the top corner of the uterus, spread to the fundus, and then downward.
During normal pregnancy, the uterus contracts intermittently but the contractions are not strong enough to overcome the resistance of a normal cervix and do not lead to its dilation.
The contractions of pregnancy become more frequent towards full term and get more painful and noticeable.
A multipara may have such ‘false pains’ for some days before the onset of true labour. They may come to hospital too early thinking they are in established labour. This is what is referred to as ‘false labour’.
Uterine Action
By the end of pregnancy the uterus is divided into two anatomically distinct segments, known as the upper and the lower uterine segments.
The upper uterine segment is a thick muscular, contractile area from where the contractions begin.
The longitudinal fibers retract, pulling on the lower segment and causing it to stretch, pushing the head down.
The lower uterine segment is thinner and develops from the isthmus of the uterus about eight to ten centimeters in length and is prepared for distension and/or dilatation.
The lower segment stretches when being pulled by the longitudinal fibres. The force applied by the descending head or breech also aids the stretching.
The retraction ring which is an imaginary ridge, forms between the upper and the lower uterine segment.
It is present in every labour and is perfectly normal as long as it is not marked enough to be visible above the symphysis pubis.
Fundal Dominance
During a contraction the uterus feels hard to touch. At the beginning of the process, contractions are painless and involuntary, and are controlled by the nervous system under the influence of endocrine hormones.
The contraction starts at the upper part of fundus, spreading across, and by the time they reach the lower fundus, they last longer and are very intense.
The peak of the contraction is reached simultaneously over the whole uterus and fades from all parts together. This pattern allows the cervix to dilate and the contracting fundus to expel the foetus.
Polarity
Polarity describes the neuromuscular harmony between the two poles or segments of the uterus throughout labour.
The upper pole contracts strongly and retracts to expel the foetus.
The lower pole contracts slightly and dilates to allow expulsion of the foetus to take place.
Contraction and Retraction
When labour starts, approximately 280 days from the first day of the last menstrual period, the contractions change in character. They become regular and more painful.
Labour contractions differ from those of pregnancy in that they are followed by retraction.
This is characteristic of uterine muscle in labour.
The contracted muscle does not return to its original length when the contraction passes off.
Each succeeding contraction leads to further shortening of the muscle fibres so that the uterine cavity becomes smaller and smaller.
When talking about contractions, you as a midwife are concerned with three factors, namely the strength, the duration and the frequency of the contraction.
When you talk of the strength of a contraction, you identify it as one of three categories: weak, fair or fairly strong, and strong.
The strength of a contraction is measured according to the time it has taken.
Thus, a contraction which takes 30 seconds is said to be weak, one that takes 30 to 40 is said to be fair or fairly strong and one that lasts for 40 to 60 seconds is said to be strong.
The duration refers to the time taken by a contraction, for example a weak contraction lasts for 10 to 30 seconds.
Frequency, on the other hand refers to the number of intervals between one contraction and the next.
If a mother has one contraction after every 45 minutes, the frequency is written as 1:45.
The Shortening and Dilation of The Cervix
Before labour begins, the cervix of a primagravida is a thick hard cone which protrudes into the vagina.
The canal is at least one inch long.
When labour begins the strongly contracting upper segment of the uterus starts retracting and getting shorter, while the thinner lower segment of the uterus gets pulled away from the presenting part. This stretches the lower segment.
The latter, in turn pulls the internal Os. This dragging away of the internal Os from the presenting part starts dilating the upper part of the cervical canal.
This goes on until the canal is shorter and shorter and finally there is no canal at all.
The canal becomes part of the uterine cavity with only the undilated external Os and the thinly stretched cervix separating this cavity from the vagina. When this happens, we say the cervix has been ‘effaced’ or ‘taken up’
In a primigravida the cervix usually becomes almost fully effaced before any dilation takes place, while in multiparous women the two processes take place together.
The cervix of a multipara might be already effaced and be dilated enough to admit a finger internal Os even before labour starts.
These signs of labour are assessed by doing a vaginal examination, though with experience, you can also get a good idea by doing a rectal examination.
As a midwife, the way you guide a mother has a great influence on the progress of her labour.
The Show
Throughout pregnancy the cervical canal is sealed by a plug of mucus known as an operculum. Together with the intact membranes this prevents organisms ascending into the uterine cavity.
When labour starts, the internal Os is pulled away from the foetal membranes and the canal is opened up. This releases the mucous plug which oozes out of the vagina mixed with a little blood. This is called the ‘show’.
The Stages of Labour
Labour is divided into four stages, although in real practice, the process is a continuous one and change from one stage to the other may not be clearly obvious. The four stages of labour are:
➢First stage,
➢ Second stage
➢Third stage
➢Fourth stage
The First Stage Of Labour
This is known as the stage of cervical dilatation.
This stage begins when regular, painful uterine contractions start and is detected clinically by the thinning and effacement of the cervix, followed by its dilatation.
The normally thick cervix becomes thinned out and stretched over the presenting part.
The first stage is completed when the cervix is fully dilated and the presenting part starts being expelled.
This stage has two phases, known as the latent and the active phase.
The contractions of the uterus dilate the cervix.
The dilatation of the internal Os causes the separation of the chorion from the deciduaclosest to it.
A small bag of membranes is formed and is forced into the internal os by the intrauterine pressure.
At the beginning of each contraction, a little more amniotic fluid is forced into the bag of membranes. The head of the foetus then comes down like a ball valve and separates the amniotic fluid above it from that in the bag.
The bag of membranes may remain intact until nearly the end of the first stage.
However, even if the membranes rupture early the cervix will still become dilated as it is drawn up over the presenting part by the retraction of the upper segment.
During the first stage, the foetus does not move downwards to any great degree. When a certain amount of fluid has left the uterus after the membranes have ruptured, a new form of pressure comes into play, namely foetal axis pressure. The upper pole of the fetus.
The upper pole of the foetus, in the breech, is pressed on by the fundus of the uterus, while the lower pole is pressed down onto the lower segment and cervix.
Should the membranes rupture early, foetalaxis pressure will operate at an early stage.
In modern practice, the membranes are often deliberately ruptured during labour because this is believed to encourage more efficient uterine action and shorten labour.
You should be cautious carrying out this procedure in this era of HIV.
The duration of the latent phase of labour need not be defined too accurately.
Dilation of the cervix from 0 to 3cm can take six hours, but slower progress may be normal and is perfectly acceptable provided that the woman is comfortable and in no way distressed.
Between 3 and 10cm dilatation (that is in the active phase of labour) the cervix should dilate at a rate of about 1 cm per hour, giving a theoretical duration of seven hours for this phase of labour in both primiparous and multiparous women.
During the early part of the latent phase the pains may not be very severe but towards the end of the active phase they are often very distressing, constituting the most painful part of labour.
Vomiting and reflex shivering are common at the end of the active phase of the first stage of labour.
By now the membranes have ruptured. If the membranes remain intact when the cervix is fully dilated, the onset of the expulsive stage may be delayed.
This is because the cervix does not receive the pressure of the head, which helps to stimulate the uterus to increase its activity.
If the membranes remain intact after full dilatation, they should be ruptured with toothed forceps or a sterile plastic amnihookduring a contraction.
Second Stage Of Labour
This starts with the full dilatation of the cervix and the expulsion of the presenting part and finishes with the complete delivery of the baby.
As you know, there may be very little descent of the foetus during the first stage. However, in the second stage, the resistance offered by the lower uterine segment and the cervix has been overcome and the presenting part can be pushed down onto the pelvic floor.
The resistance of the pelvic floor then has to be overcome by uterine contractions, aided by the action of the voluntary muscles of the abdominal wall and the diaphragm.
In the absence of an effective epidural block, full dilatation of the cervix is accompanied by a bearing down sensation during contractions and women are usually encouraged to push.
As the contraction comes on, the woman takes a deep breath, then holds it and subsequently bears down with all the force of her abdominal.
These partly voluntary, partly reflex expulsive efforts place the foetus under additional stress and pushing should, therefore, not be allowed to continue for more than one hour.
If delivery is not imminent, assistance in the form of forceps delivery or even a Caesarean section may be necessary.
Third Stage Of Labour
This stage commences immediately after the birth of the baby. It includes the delivery of the placenta and membranes as well as the control of bleeding.
At this stage the uterus contracts down to follow the body of the foetus as it is being born. As the cavity of the uterus becomes smaller, the area of the placental site is diminished.
The placenta is then cut off from the spongy layer of the decidua basalis. Further uterine contractions expel the placenta from the upper segment into the lower segment and through the vaginal vault.
This process, whereby the placenta leaves the upper segment to the lower segment and through the vagina, is referred to as separation and descent.
Fourth Stage Of Labour
This is the period from the delivery of placenta and membranes to the end of the first hour postpartum. The uterus is firm at level of two fingers breadth above the umbilicus. Restoration of physiological stability is established.
During this period myometrial contractions and retraction, accompanied by vessel thrombosis, operate effectively to control bleeding from the placenta site.
Failure of this mechanism could result in excessive blood loss (postpartum haemorrhage(PPH)) that could be life threatening.
The mother should be closely observed for haemorrhage, urine retention or hypotension.
The mother and child relationship should be initiated and encouraged, as it has an effect to the subsequent quality of their relationship and bonding.