Process of Labour
Labour is the expulsion or extraction of viable fetus out of the uterus. Delivery may be vaginal (either spontaneous or aided) or it may be abdominal. Labour is a series of events that takes in the genital organs in an effort to expel the viable products of conception out of the uterus through the vagina. Usually it occurs between 38-42 weeks of pregnancy. If labour occurs before 37 weeks, it is termed as preterm labour. Expulsion of conceptual products before 28 weeks is called abortion.
Normal labour (Eutocia) occurs at term and is spontaneous in onset with the fetus presenting by the head. The process is completed within 12-18 hours and no complications arise by which the fetus, placenta and membrane are expelled through the birth canal. Dystocia is the term used to denote a difficult labour
Factors affecting Labour Process
- Passages: The passage is the adequate pelvic dimension, pelvic floor muscles, soft tissues of the cervix and vagina.
- Passenger: The passenger is the adequate fetal dimensions like the fetal lie, fetal size, fetal position, fetal presentation and attitude.
- Powers: The mother exhibits both voluntary and involuntary powers to expel the fetus. Primary powers are the uterine contractions and secondary powers are the maternal efforts taken to expel the fetus with the help of abdominal muscles and the diaphragm.
- Position: Upright position helps in descent of the presenting partand also reduces incidence of umbilical cord compression and improves cardiac workload
- Psyche of the mother: Emotional status of the mother also influences the outcome of labour.
Theories of Labor Onset
Labor normally begins when a fetus is sufficiently mature to cope with extrauterine life yet not too large to cause mechanical difficulty with birth. The trigger that converts the random, painless Braxton Hicks contractions into strong, coordinated, productive labor contractions is unknown. In some instances, labor begins before a fetus is mature (preterm birth). In others, labor is delayed until the fetus and the placenta have both passed beyond the optimal point for birth (postterm birth).
Although a number of theories have been proposed to explain why labor begins, it is believed that labor is influenced by a combination of factors originating from the mother and the fetus. The following are the causes for the onset of labor:
- Uterine muscle stretching: The excessive stretching of the myometrium due to growing fetus results in release of prostaglandins
- Pressure on the cervix, which stimulates the release of oxytocin from the posterior pituitary
- Oxytocin stimulation, which works together with prostaglandins to initiate contractions
- Change in the ratio of estrogen to progesterone (increasing estrogen in relation to progesterone stimulates uterine contractions)
- Placental age, which triggers contractions at a set point
- Rising fetal cortisol levels, which reduce progesterone formation and increase prostaglandin formation
- Fetal membrane production of prostaglandin, which stimulates contractions
- Uterus becomes stretched and the pressure increases causing physiological changes.
- As pregnancy advances there is a gradual rise in oxytocin level (a hormone which is responsible for uterine contraction).
- There is increased production of prostaglandin by fetal membranes and uterine decidua. The mutual coordinated effects of oxytocin and prostaglandin initiate the rhythmic contractions of true labour.
Signs of Labor
Signs of true labor involve uterine and cervical changes. The more a woman knows about true labor signs, the better, because then she will be better able to recognize them. This is helpful both to prevent preterm birth and for the woman to feel secure knowing what is happening during labor.
In primiparas, lightening, or descent of the fetal presenting part into the pelvis, occurs approximately 10 to 14 days before labor begins. This changes a woman's abdominal contour, because the uterus becomes lower and more anterior. Lightening gives a woman relief from the diaphragmatic pressure and shortness of breath that she has been experiencing and in this way “lightens” her load. Lightening probably occurs early in primiparas because of tight abdominal muscles. In multiparas, it is not as dramatic and usually occurs on the day of labor or even after labor has begun. As the fetus sinks lower in the pelvis, the mother may experience shooting leg pains from the increased pressure on the sciatic nerve, increased amounts of vaginal discharge, and urinary frequency from pressure on the bladder.
- Increase in Level of Activity
A woman may awaken on the morning of labor full of energy, in contrast to her feelings of chronic fatigue during the previous month. This increase in activity is related to an increase in epinephrine release that is initiated by a decrease in progesterone produced by the placenta. Additional epinephrine prepares a woman's body for the work of labor ahead.
- Braxton Hicks Contractions
In the last week or days before labor begins, a woman usually notices extremely strong Braxton Hicks contractions, which she may interpret as true labor contractions. Primiparas may have great difficulty in distinguishing between the two forms of contractions. A woman may be admitted to the labor unit of a hospital or birthing center because false contractions so closely simulate true labor.
- Ripening of the Cervix
Ripening of the cervix is an internal sign seen only on pelvic examination. Throughout pregnancy, the cervix feels softer than normal, similar to the consistency of an earlobe (Goodell's sign). At term, the cervix becomes still softer (described as “butter-soft”). Ripening is an internal announcement that labor is very close at hand.
- Uterine Contractions
The surest sign that labor has begun is productive uterine contractions. Because contractions are involuntary and come without warning, their intensity can be frightening in early labor. Helping a woman appreciate that she can predict her pattern and therefore can control the degree of discomfort she feels by using breathing exercises offers her a sense of control.
As the cervix softens and ripens, the mucus plug that filled the cervical canal during pregnancy (operculum) is expelled. The exposed cervical capillaries seep blood as a result of pressure exerted by the fetus. The blood, mixed with mucus, takes on a pink tinge and is referred to as “show” or “bloody show.” Women need to be aware of this event so that they do not think they are bleeding abnormally.
- Rupture of the Membranes
Labor may begin with rupture of the membranes, experienced either as a sudden gush or as scanty, slow seeping of clear fluid from the vagina. Some women may worry if their labor begins with rupture of the membranes, because they have heard that labor will then be “dry” and that this will cause it to be difficult and long. Actually, amniotic fluid continues to be produced until delivery of the membranes after the birth of a fetus, so no labor is ever “dry.” Early rupture of the membranes can be advantageous if it causes the fetal head to settle snugly into the pelvis; this can actually shorten labor.
Two risks associated with ruptured membranes are intrauterine infection and prolapse of the umbilical cord, which can cut off the oxygen supply to the fetus. In most instances, if labor has not spontaneously occurred by 24 hours after membrane rupture and the pregnancy is at term, labor is induced to help reduce these risks.
During the last few weeks of pregnancy number of changes occur in women.
· Walking is more difficult as the fetal head enters into the pelvis
· There is frequency of micturition
· There is backache due to relaxation of sacroiliac of joints
· There may be spurious or false pains
Differentiation Between True and False Labor Contractions
· Begin and remain irregular.
· Begin irregularly but become regular and predictable.
· Felt first abdominally and remain confined to the abdomen and groin.
· Felt first in lower back and sweep around to the abdomen in a wave.
· Often disappear with ambulation and sleep.
· Continue no matter what the woman's level of activity.
· Do not increase in duration, frequency, or intensity.
· Increase in duration, frequency, and intensity.
· Do not achieve cervical dilatation.
· Achieve cervical dilatation.
Features of true labour pain:
1. Uterine contractions (labour pains) occur in regular intervals,
2. Intensity of labour pain increases with time
3. The labour pain is located in back and abdomen.
4. Walking intensifies the pain.
5. Pain is not affected by mild sedatives.
6. Pain results in progressive, cervical dilation
Stages of labour:
First stage of labour:
This is the stage of dilatation of the cervical OS. It begins with the onset of true labour contractions to full dilatation of the cervix. Duration of first stage is an average of 13 hours for nullipara and 7.5 hours for multipara. The first stage is clinically manifested by progressive uterine contraction, progressive taking up of the cervix and ultimate rupture of membranes.
Second stage of labour:
It is the stage of fetal expulsion. It begins with full dilation of cervical OS and ends with the birth of the baby. Second stage lasts for one to one and half hours for nullipara and 20 to 45 minutes in multipara.
Third stage of labour:
It is the stage of separation and expulsion of the placenta and membranes. It begins with birth of the baby until the expulsion of placenta and membranes. The third stage may last from few minutes to thirty minutes.
The fourth stage lasts from the delivery of placenta and membranes until the postpartum condition of the women has become stabilized. This stage is usually one hour after delivery. In this stage the mother must start breast-feeding her infant.