Obstetrics Simplified - Diaa M. EI-Mowafi

Preterm Labour

Definition

It is onset of labour before completed 37 weeks of pregnancy.

Incidence

5-10%.

Aetiology

  • Maternal causes:
    • Medical disorders:
      • Preeclampsia.
      • Chronic nephritis.
      • Anaemia and malnutrition.
    • Antepartum haemorrhage:
      • Placenta praevia.
      • Abruptio placentae.
    • Uterine anomalies:
      • Septate uterus.
      • Incompetent cervix.
      • Fibroid uterus.
    • Psychological or hormonal.
  • Foetal causes:
    • Congenital anomalies.
    • Intrauterine foetal death.
    • Polyhydramnios.
    • Multiple pregnancy.
    • Rh-isoimmunization.
    • Premature rupture of membranes.
  • Idiopathic.

Risk of Prematurity

  • Birth trauma: particularly intracranial haemorrhage which is aggravated by hypoprothrombinaemia and capillary fragility present in prematures.
  • Respiratory distress syndrome (RDS):
    • occurs due to deficient pulmonary surfactant which helps distension of the alveoli. A structureless hyaline membrane will develop within the alveolar ducts and atelectasis of the alveoli occurs.
    • Dyspnoea and cyanosis develops 1-2 hours after delivery and death occurs after about 30 hours.
    • RDS is seen also in infants;
      • to diabetic mothers,
      • delivered by caesarean sections, or
      • had intrapartum asphyxia.
    • Treatment: oxygen and 8.4 % sodium bicarbonate infusion to combat acidosis.
  • Hypothermia as a result of:
    • Decreased heat production due to;
      • reduced muscle activity and hypoglycaemia.
    • Increased heat loss due to;
      • large surface area relative to body weight,
      • lack of insulating fat,
      • immaturity of the heat regulating center.
  • Infection especially respiratory due to:
    • immaturity of the immune mechanism,
    • susceptibility of the delicate tissues to trauma.
  • Haematological disorders:
    • Anaemia due to:
      • impaired haemopoiesis,
      • increased RBCs destruction,
      • poor iron stores in the liver which are filled in the last weeks of pregnancy.
    • Hypoprothrombinaemia: due to liver immaturity this is in addition to capillary fragility increase the liability for haemorrhage.
    • Hyperbilirubinaemia due to:
      • liver immaturity and
      • increased RBCs destruction.
  • Malnourishment due to:
    • weak suckling,
    • weak digestion and
    • liver immaturity.
  • Rickets and impaired mental development occurs more frequently in children who were prematures.

Prediction

Recently, it has been reported that detection of foetal fibronectin, which is a glycoprotein synthesized in the chorio-decidual interface, in the cervico-vaginal sample is a predictor of imminent preterm labour.

Diagnosis

  • Uterine contractions of:
    • frequency every 10 minutes or less,
    • duration at least 30 seconds and
    • continue for at least one hour.
  • Uterine contractions of whatever the frequency and duration but with:
    • rupture membranes,
    • effacement 75% or more, or
    • cervical dilatation ≥3 cm in primigravida and ≥4 cm in multigravida.

Management

Prophylactic management

  • Adequate rest for high risk patients.
  • Improve health and nutrition.
  • Discourage cigarette smoking.
  • Treatment of cervical incompetence by circulage in the second quarter of pregnancy.

Preventive management

The aim is to inhibit labour till completed 37 weeks’ gestation or at least till the foetal lung maturity is ensured . This may be achieved by acting on one or more of the following theories of labour.

  • Neuromuscular:
    • Sedation: as diazepam.
    • Ethyl alcohol (Ethanol).
    • Sympathomimetic drugs: as ritodrine and isoxuprine.
    • Receptor blockers: as phenoxybenzamine.
  • Hormonal:
    • Betamethazone:
      • 4 mg betamethazone IM every 8 hours for 48 hours can cause:
        • decrease oestrogen synthesis by depressing the production of its precursor from the foetal adrenal gland.
        • inhibition of prostaglandin synthesis.
        • acceleration of foetal lung maturity.
    • Prostaglandin inhibition: e.g. indomethacin.
    • Oxytocin inhibition by:
      • Hydration with a rapid IV infusion of 0.9% Nacl (normal saline) in a rate of 120 ml/hour. This will decrease the release of oxytocins as well as antidiuretic hormone from the posterior pituitary.
      • Ethyl alcohol.
  • Mechanical:
    • Rest in bed: to reduce the mechanical stimuli from the pressure of the presenting part on the lower uterine segment.
    • Cervical cerclage: it is of value in prevention of abortion and preterm labour if done at 14-16 weeks’ gestation but not so later on.

Amniocentesis: was advocated by some authors to reduce the mechanical distension of the uterus in polyhydramnios. The drainage should be slowly aspirating 1 litre of amniotic fluid over 3-4 hours as sudden drop of uterine volume may initiate uterine contractions and causes abruptio placentae.

Management of inevitable preterm labour

Inevitable labour occurs when there is frequent labour pain (> 10 contractions/hour) and the cervix is > 3 cm in primigravidae or > 4 cm in multigravidae.

Intranatal care:

  • Hospital delivery: is indicated with an available incubator.
  • Anaesthesia and analgesia: It is better to avoid the systemic ones that can depress the foetal respiratory center. Epidural or local infiltration anaesthesia or analgesia is the best.
  • Vitamin K1: 10 mg IM to the mother during labour to guard against foetal haemorrhage.
  • Method of delivery:
    • Vertex presentation: vaginal delivery is allowed with,
      • continuous FHR monitoring and
      • generous episiotomy ± outlet forceps to avoid compression and sudden decompression of the foetal head.
    • Breech presentation: is best delivered by caesarean section as vaginal delivery causes sudden compression of the after-coming unmoulded head resulting in intracranial haemorrhage.

Postnatal care:

  • Air way: suction and oxygen if needed.
  • Incubation: is indicated if the birth weight is less than 2.5 kg.
    • The baby is placed on his side with the head slightly lower down.
    • Temperature of the incubator is between 32-36oC.
    • Humidity of 70%,
    • Oxygen concentration not more than 30% to avoid retrolental fibroplasia and blindness.
    • Minimal handling and no bathing but skin can be rubbed with olive oil every other day.
  • Antibiotics: prophylactic antibiotic as ampicillin to protect against infection.
  • Feeding: Breast milk is given as normal if the baby can suck, otherwise the expressed milk can be given by a dropper, spoon or nasogastric tube.
  • Vitamins and iron:
    • Vitamin K 1mg IM is given to the neonate if it was not given to the mother during labour.
    • Iron and vitamins: can be given at the age of 2-3 weeks.

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Edited by Aldo Campana,