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FIRST STAGE OF NORMAL LABOR
Written by : Dr.M.D.Mazumdar, MD
Onset of Labor : There are three classical signs by which the onset of labor is diagnosed. Any one of the signs is enough to diagnose the onset of labor - it is not necessary to get all three signs.
- Painful Uterine Contractions: The onset of labour is characterized by painful, intermittent, involuntary and co-ordinated uterine contractions which cannot be relieved by medicines or rest. Each word in the description has its own importance.
Some women get uterine contractions in late pregnancy which they often mistake for onset of labor. But the contractions are usually not regular, does not increase gradually in intensity and are relieved by medicines or rest. These are 'false labor pains'.
Braxton Hicks contractions occur throughout pregnancy and are not related to labor pains.
- Expulsion of Show or Mucus Plug: During pregnancy, the cervix which is the mouth of the uterus is filled with dense mucus that seals it to some extent. As the cervix begins to thin out and open to allow the baby to be born, this mucus is expelled through the vagina.
There is also some amount of bleeding from blood vessels that rupture when the cervix dilates. These present at the vaginal opening as blood stained mucus. This blood stained mucus is called 'show'or 'mucus plug'.
The mucus plug may consist of thin or thick mucus. It may be just bloodstained in some women, resulting in brownish vaginal discharge. But in others , there may be frank bleeding at the time of expulsion of the mucus plug.
- Rupture of Membranes: In many women, the onset of labor is signified by the rupture of the bag of waters (rupture of membranes) without any prior abdominal pain. The rupture of the membranes may occur with a sudden gush of waters, or with only a thin trickle that is barely enough to soak the underwears.
Usually, leakage of water is more in the lying down position. Standing or sitting up causes the head of the fetus to plug the mouth of the uterus and prevents outflow of the amniotic fluids (waters).
PHASES OF THE FIRST STAGE OF NORMAL LABOUR
The painful contractions increase in frequency,intensity, duration and force as labor advances. The cervix also dilates simultaneously from 0 cms to 10 cms (full dilation) at the end of the first stage of labour.
- Phase I or the Latent Phase of Labor: Uterine contractions at this phase may be very mild . They can be irregular and not forceful enough to cause much pressure on the cervix. During this phase, the cervix slowly becomes shorter and softer. This is known as 'Effacement'.
Dilation of the cervix occurs from 0 cm to 4 cm. The frequency of the uterine contractions at this stage is from 1-3 per 10 minutes in normal labour and each contraction lasts for less than a minute. The uterus may become firm and more prominent with every contraction.
In some women, the labor pains start at the back. This is more likely if the head of the fetus is more posteriorly placed and presses on the mother's spine or ligaments.
- Phase II or the Active Phase of Labor: This is the phase where the uterus contracts more frequently and the pain is maximum. Uterine contraction occurs after every 3-5 minutes and lasts for more than a minute. The uterus becomes hard and more prominent as the pain increases and softer as the uterus relaxes. The pains sometimes start at the back and radiates down to the thighs. Later on, at the end of this stage, the pains come even more frequently and appear to run into each other in quick succesion.
The cervix dilates from 4 cm to 8 cm. Women whose waters have not ruptured at the onset of labour, can experience a gush of water flowing out of the vagina at this stage.
- Phase III or the Transitional Phase of Labor: This phase is called the transitional phase because it marks the transition from the first stage of labour to the second stage of labour. The cervix dilates from 8 cm to 10 cm. At full dilatation at the end of the first stage of labour, the cervix is about 10 cm (4inches) in diameter. Since the maximum diameter of the fetal head is also 10 cm when it is in a normal position, the baby can be born easily through the cervix.
MANAGEMENT OF FIRST STAGE OF NORMAL LABOUR
The principle of management of this stage is to prepare the patient to have a safe vaginal delivery and to carefully monitor the vital signs for eary detection of any deviation from the normal.
- Thorough general and obstetrical examination is done as soon as labor pains start to plan for an uncomplicated labour, to check for a normal fetal heart rate and to exclude any cephalopelvic disproportion (where the diameter of the head is larger than the mother's pelvis).
- Antiseptic dressing of the external genitals, inner part of the thighs, and lower part of the abdomen.
- Bowel must be evacuated - with an enema, if necesary. A full bowel can hamper the downward movement of the head.
- Evacuation of the bladder with a catheter if the patient is unable to pass urine herself.
- Nourishment is provided by liquid food which can be easily suctioned out should the need for anesthesia and operative delivery (cesarian section) arise.
- During the active phase of labour when the pains are severe, the patient is encouraged to lie down in bed to prevent injuring herself. Lying in the left lateral position wil increase the blood flow to the contracting uterus and to the fetus.
- When pain is less, she can walk around or sit up in any position she feels comfortable.
Relief of pain:
- In the early part of labour, the patient may be allowed injectible analgesics, but these may cause depression of the baby and is best avoided if there are less than 3 hours before delivery.
- In later part of the first stage and early second stage, inhalation anesthesia by mixing an equal part of oxygen and an anesthetic agent can be used.
- Epidural anesthesia (anesthetic through a needle in the spine) is used when complete pain relief is needed. But the disadvantage is that the patient cannot move about freely. There is also a risk of prolongation of the second stage as the patient cannot bear down. The operative delivery rate (Cesarian Section, vacuum extraction etc.) increases.
Labour monitoring :
When the cervix is fully dilated (10 cms) it signifies that the second stage has started and the patient is shifted to the labor room from the observation room.
- Maternal vital signs like pulse, blood pressure, duration and frequency of contractions are noted regularly.
- Fetal Status is recorded by counting the fetal heart rate every two hours initially, increasing the frequency in the later stages. Continuous electronic recording of the heart rate and intrauterine pressure can be employed but this has the disadvantage of restricting the movements of the patient. So it should ideally only be used in high risk pregnancies.
- Uterine contractions – Frequency and duration are recorded at regular intervals.
- Rupture of membranes : As soon as the bag of membranes ruptures / bursts, the liquor amnii is checked for its colour. Liquor stained brown or black signifies that the fetus has passed meconium (fetal stool) in the uterus and is in danger. Immediate delivery - whether vaginal or cesarian section - is a must.
- Fetal Scalp blood sampling : Fetal blood is examined for its oxygen content. Lowered oxygen saturation signifies that the foetus is not receiving adequate oxygen and should be delivered as soon as possible. Fetal scalp blood sampling is done only in high risk cases.
- Periodic vaginal examinations to determine the rate of dilation of the cervix.
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