Preterm labour and preterm rupture of the membranes
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When you have completed this unit you should be able to:
- Define preterm labour and preterm rupture of the membranes.
- Understand why these conditions are very important.
- Understand the role of infection in causing preterm labour and preterm rupture of the membranes.
- List which patients are at increased risk of these conditions and what preventive measures should be taken.
- Diagnose preterm labour and preterm rupture of the membranes.
- Initiate the correct management and appropriate referral of patients.
Preterm labour and preterm rupture of the membranes
###5-1 What is preterm labour?
Preterm labour is diagnosed when there are regular uterine contractions before 37 weeks of pregnancy, together with either of the following:
- Cervical effacement and/or dilatation.
- Rupture of the membranes.
5-2 What is preterm rupture of the membranes?
Preterm rupture of the membranes is diagnosed when the membranes rupture before 37 weeks, in the absence of uterine contractions.
5-3 What is prelabour rupture of the membranes?
Prelabour rupture of the membranes is defined as rupture of the membranes for at least one hour before the onset of labour in a term pregnancy.
5-4 How should you diagnose preterm labour if the gestational age is unknown?
Preterm labour is diagnosed if the estimated fetal weight is below 2500 g. The symphysis-fundus height will be less than 35 cm.
5-5 Why are preterm labour and preterm rupture of the membranes important?
Preterm labour and preterm rupture of the membranes are major causes of perinatal death because:
- Preterm delivery, especially before 34 weeks, commonly results in the birth of an infant who develops hyaline membrane disease and other complications of prematurity.
- Preterm labour and preterm rupture of the membranes are often accompanied by bacterial infection of the membranes and placenta, that may cause complications for both the mother and the fetus. The mother and fetus may develop severe infection, which is life threatening.
5-6 What is the commonest known cause of preterm labour and preterm rupture of the membranes?
In many cases the cause is unknown, but increasing evidence points to infection of the membranes and placenta as the commonest known cause of both preterm labour and preterm rupture of the membranes.
Infection of the membranes and placenta is the commonest recognised cause of preterm labour and preterm rupture of the membranes.
5-7 What is infection of the membranes and placenta?
Infection of the membranes and placenta causes an acute inflammation of the placenta, membranes and decidua. This condition is called chorioamnionitis. It may occur with intact or ruptured membranes.
Bacteria from the cervix and vagina spread through the endocervical canal to infect the membranes and placenta. Later these bacteria may colonise the liquor, from where they may infect the fetus.
Infection of the membranes and placenta (chorioamnionitis) may occur with either intact or ruptured membranes.
5-8 What is the clinical presentation of chorioamnionitis?
Usually chorioamnionitis is asymptomatic (subclinical chorioamnionitis) and, therefore, the clinical diagnosis is often not made. However, the following signs may be present:
- Fetal tachycardia.
- Maternal pyrexia and/or tachycardia.
- Tenderness of the uterus.
- Drainage of offensive liquor, if the membranes have ruptured.
If any of the above signs are present, a diagnosis of clinical chorioamnionitis must be made.
5-9 What factors may predispose to chorioamnionitis?
- Rupture of the membranes.
- Exposure of the membranes due to dilatation of the cervix.
- Coitus during the second half of pregnancy.
However, in many cases, the factors that result in chorioamnionitis are not known.
5-10 Can chorioamnionitis cause complications during the puerperium?
Yes, it can cause serious problems.
- Bacteria that have colonised the amniotic fluid, may infect the fetus and the infant may present with signs of infection (congenital pneumonia or septicaemia) at or soon after birth.
- Chorioamnionitis may cause infection of the genital tract (puerperal sepsis) which, if not treated correctly, may result in septicaemia, the need for hysterectomy, and possibly in maternal death. These complications can usually be prevented by starting a course of broad-spectrum antibiotics (e.g. intravenous ampicillin plus metronidazole), as soon as the diagnosis of clinical chorioamnionitis is made.
5-11 What factors other than chorioamnionitis can lead to preterm labour and preterm rupture of the membranes?
The following maternal, fetal and placental factors may be associated with preterm labour and/or preterm rupture of the membranes:
- Maternal factors:
- Pyrexia, as the result of an acute infection other than chorioamnionitis, e.g. acute pyelonephritis or malaria.
- Uterine abnormalities, such as congenital uterine malformations (e.g. septate or bicornuate uterus) and uterine myomas (fibroids).
- Incompetence of the internal cervical os (‘cervical incompetence’).
- Fetal factors:
- A multiple pregnancy.
- Congenital malformations of the fetus.
- Placental factors:
- Placenta praevia.
- Abruptio placentae.
5-12 Which patients are at an increased risk of preterm labour or preterm rupture of the membranes?
Both preterm labour and preterm rupture of membranes are more common in patients who:
- Have a past history of preterm labour.
- Have no antenatal care.
- Live in poor socio-economic circumstances.
- Smoke, use alcohol or abuse habit-forming drugs.
- Are underweight due to undernutrition.
- Have coitus in the 2nd half of pregnancy, when they are at an increased risk of preterm labour or infections.
- Have any of the maternal, fetal or placental factors listed above.
The most important risk factor for preterm labour is a previous history of preterm delivery.
5-13 What can be done to decrease the incidence of these complications?
- Take measures to ensure that all pregnant women receive antenatal care.
- Identify patients with a past history of preterm labour.
- Give advice about the dangers of smoking, alcohol and the use of habit-forming drugs.
- Advise against coitus during the late 2nd and in the 3rd trimester in pregnancies at high risk for preterm labour or preterm rupture of the membranes. If coitus occurs during pregnancy in these patients, the use of condoms must be recommended as this may reduce the risk of chorioamnionitis.
- Insert a McDonald suture at 14–16 weeks, in patients with a proven incompetent internal cervical os.
- Prevent teenage pregnancies.
- Improve the socio-economic and nutritional status of poor communities.
- Arrange that the workload of women, who have to do heavy manual labour, is decreased when they are pregnant and that an opportunity to rest during working hours is allowed.
5-14 How should you manage a patient at increased risk of preterm labour or preterm rupture of the membranes?
- Patients at increased risk must have 2 weekly vaginal examinations from 24 weeks, in order to make an early diagnosis of preterm cervical effacement and/or dilatation.
- In all women with cervical effacement or dilatation before 34 weeks, the following preventive measures can then be taken:
- Bed rest. This can be at home, except when the home circumstances are poor, in which case the patient should be referred to the hospital for admission.
- Sick leave must be arranged for working patients.
- Coitus must be forbidden.
- Advice must be given to report immediately, if contractions or rupture of the membranes occur.
- Women with preterm labour or preterm rupture of the membranes must be seen as soon as possible, and the correct measures taken to prevent the delivery of a severely preterm infant.
All patients should be told to immediately report preterm labour or preterm rupture of the membranes.
5-15 What should you do if a patient threatens to deliver a preterm infant?
- Infants born between 34 and 36 weeks can usually be cared for in a level 1 hospital.
- However, women who threaten to deliver between 28 and 33 weeks, should be referred to a level 2 or 3 hospital with a neonatal intensive care unit.
- If the birth of a preterm baby cannot be prevented, it must be remembered that the best incubator for transporting an infant is the mother’s uterus. Even if the delivery is inevitable, an attempt to suppress labour should be made, so that the patient can be transferred before the infant is born.
- The better the condition of the infant on arrival at the neonatal intensive care unit, the better is the prognosis.
Diagnosis of preterm labour and preterm rupture of the membranes
5-16 How should you distinguish between Braxton Hicks contractions and the contractions of preterm labour?
Braxton Hicks contractions:
- Are irregular.
- May cause discomfort but are not painful.
- Do not increase in duration or frequency.
- Do not cause cervical effacement or dilatation.
The duration of contractions cannot be used as Braxton Hicks contractions may last up to 60 seconds.
In contrast, the contractions of preterm or early labour:
- Are regular, at least one per 10 minutes.
- Are painful.
- Increase in frequency and duration.
- Cause effacement and dilatation of the cervix.
5-17 How should you confirm the diagnosis of preterm labour?
Both of the following will be present in a patient of less than 37 weeks gestation:
- Regular uterine contractions, palpable on abdominal examination, of at least one per 10 minutes.
- A history of rupture of the membranes, or cervical effacement and/or dilatation on vaginal examination.
5-18 How can you diagnose preterm rupture of the membranes?
- A patient of less than 37 weeks gestation will give a history of sudden drainage of liquor followed by a continual leak of smaller amounts, without associated uterine contractions.
- A sterile speculum examination will confirm the diagnosis of ruptured membranes.
- A digital vaginal examination must not be done as it is of little value in diagnosing rupture of the membranes and may increase the risk of infection.
A digital vaginal examination must not be done in preterm rupture of the membranes.
5-19 What is the value of a sterile speculum examination when preterm rupture of the membranes is suspected?
- The danger of ascending infection is not increased by this procedure.
- Observing drainage of liquor from the cervical os confirms the diagnosis of ruptured membranes.
- If no drainage of liquor is observed, drainage can sometimes be seen if the patient is asked to cough.
- If no drainage of liquor is seen, a smear should be taken from the posterior vaginal fornix with a wooden spatula to determine the pH.
- The possibility of cord prolapse can be excluded or confirmed.
- It is also important to see whether the cervix is long and closed, or whether there is already clear evidence of cervical effacement and/or dilatation.
- A patient with a profuse vaginal discharge or stress incontinence (leaking urine when coughing or laughing) may think that she is draining liquor. A speculum examination will help to confirm or rule out this possibility.
5-20 How should you test the vaginal pH?
- The pH of the vagina is acid but the pH of liquor is alkaline.
- Red litmus paper is pressed against the moist spatula. If the red litmus changes to blue, then liquor is present in the vagina, indicating that the membranes have ruptured. If blue litmus is used, it will remain blue with rupture of membranes or change to red if the membranes are intact.
5-21 How should you manage patients with preterm labour, preterm rupture of membranes and prelabour rupture of membranes?
- If the gestational age is less than 36 weeks, these patients should be referred to a level I hospital for admission. If the gestational age is less than 34 weeks, she must be referred to a level 2 hospital.
- If the gestational age is 36 weeks of more, patients can safely be delivered in a midwife obstetric unit (MOU) or district hospital. At a gestational age of 36 weeks babies will not develop the complications of preterm infants and could be discharged 6 hours following delivery with their mothers.
5-22 How will you decide that a patient is less than 36 weeks pregnant if the duration of the pregnancy is unknown?
This is done by measuring the symphysis-fundus height and by doing a complete abdominal examination. An estimated fetal weight of less than 2500 g, suggests a gestational age of less than 36 weeks. The symphysis-fundus height measurement will be less than 34 cm.
5-23 What should be done if preterm labour has been diagnosed and the patient is less than 34 weeks pregnant?
Contractions should be suppressed with nifedipine (Adalat). The patient must then be transferred as an urgent transferal to a level 2 hospital. If nifedipine is not available salbutamol (Ventolin) can be used. This measure will:
- Improve the chance of successful suppression of preterm labour at the hospital.
- Reduce the risk of a delivery before arrival at the hospital or clinic.
Infants born before 34 weeks are at increased risk of developing complications. Therefore, suppression of contractions to allow continuation of pregnancy is important in these cases. The earlier the suppression of contractions is started the better the chance of successful suppression will be.
5-24 How would you decide that a patient is less than 34 weeks pregnant if the duration of the pregnancy is unknown?
This is done by measuring the symphysis-fundus height and by doing a complete abdominal examination.
Labour must be suppressed if the estimated fetal weight is less than 2000 g as this suggests an estimated gestational age of less than 34 weeks. The symphysis-fundus height measurement will be less than 33 cm.
5-25 How should you give nifedipine for the suppression of preterm labour?
Three nifedipine (Adalat) 10 mg capsules (total 30 mg) should be taken by mouth. If there are still contractions with cervical dilatation and effacement 3 hours after the initial dose, a follow-up dose of 20 mg must be given.
5-26 What are the contraindications to the use of nifedipine in suppressing labour?
Nifedipine (Adalat) cannot be used for the suppression of preterm labour if patients have hypertension, e.g. suffering from any of the hypertensive disorders of pregnancy.
5-27 How should you use salbutamol for the suppression of preterm labour?
- A half an ampoule (0.5 ml = 250 μg) of salbutamol (Ventolin) is diluted with 9.5 ml of sterile water in a 10 ml syringe and administered slowly intravenously (0.5 ml per minute) while the maternal heart rate is carefully monitored for a tachycardia.
- The patient must be warned that salbutamol causes tachycardia (palpitations).
5-28 What are the contraindications to the use of salbutamol in suppressing labour?
- Heart valve disease. The use of salbutamol (or another beta2 stimulant), can endanger the patient’s life, especially if she has a narrowed heart valve, e.g. mitral stenosis.
- A shocked patient.
- A patient with a tachycardia, e.g. as the result of an acute infection.
5-29 What advice should you give to a woman who has delivered a preterm infant?
- She should be seen at a level 2 hospital before her next pregnancy to be assessed for possible causes, e.g. cervical incompetence.
- She must book early in any future pregnancy.
Case study 1
A patient, 32 weeks pregnant, presents with regular painful uterine contractions. She is apyrexial and appears clinically well. On vaginal examination, the cervix is 4 cm dilated. The fetal heart rate is 138 beats per minute with no decelerations.
1. Is the patient in true or false labour? Give the reasons for your diagnosis.
She is in true labour because she is getting regular painful contractions and her cervix is 4 cm dilated.
2. What signs exclude a diagnosis of clinical chorioamnionitis?
The patient is apyrexial, clinically well and has a normal fetal heart rate.
3. Why could chorioamnionitis still be the cause of her preterm labour?
Because chorioamnionitis is often asymptomatic (subclinical chorio-amnionitis).
4. Would you allow labour to continue or would you suppress labour prior to referring the patient to the hospital?
Labour should be suppressed because the pregnancy is of less than 34 weeks duration.
5. How should labour be suppressed?
Labour must be suppressed using nifedipine (Adalat) or salbutamol (Ventolin).
Case study 2
A patient, who is 36 weeks pregnant, reports that she has been draining liquor since earlier that day. The patient appears well, with normal observations, no uterine contractions and the fetal heart rate is normal.
1. Would you diagnose rupture of the membranes on the history given by the patient?
No, other causes of fluid draining from the vagina may cause confusion, e.g. a vaginitis or stress incontinence.
2. How would you confirm rupture of the membranes?
A sterile speculum examination should be done. If there is no clear evidence of liquor draining, the vaginal pH must be determined with Litmus paper to identify liquor.
3. Why should you not perform a digital vaginal examination to assess whether the cervix is dilated or effaced?
A digital vaginal examination is contra-indicated in the presence of rupture of the membranes if the patient is not already in labour, because of the risk of introducing infection.
4. Is this patient at high risk of having or developing chorioamnionitis?
Yes. The preterm prelabour rupture of the membranes may have been caused by chorioamnionitis. In addition, all patients with ruptured membranes are at an increased risk of developing chorioamnionitis.
5. Should the patient be referred to a level I (district hospital/MOU) or level II hospital? Give your reasons.
She is 36 weeks pregnant and there are no signs of chorio-amnionitis. She should be referred to a level I hospital or MOU.
Case study 3
An unbooked patient presents at a primary care clinic with a 5 day history of ruptured membranes. She is pyrexial with lower abdominal tenderness and is draining offensive liquor. She is uncertain of her dates but abdominal examination suggests that she is at term. Treatment has been started with oral ampicillin.
1. What signs of clinical chorioamnionitis does the patient have?
She is pyrexial, with lower abdominal tenderness and she has offensive liquor.
2. How should the patient be managed?
There is danger of spreading infection in both the mother and fetus if the infant is not delivered. The patient must be referred to the next level of care as an urgent case.
3. Is oral ampicillin the correct initial treatment while waiting for the transfer? Give your reasons.
Chorioamnionitis may result in a severe infection of the genital tract that may cause a maternal death. These complications can usually be prevented by starting broad-spectrum antibiotics (ampicillin and metronidazole) as early as possible. The ampicillin must be given intravenously.
4. Why is the infant at increased risk for neonatal complications?
The chorioamnionitis has already spread to the liquor as this is offensive. Therefore, the fetus may also be infected and may present with congenital pneumonia or septicaemia at birth.