Premature Labour

Definitions

Rupture of membranes (ROM): The amniotic sac has ruptured.

Spontaneous rupture of membranes (SROM): The amniotic sac has ruptured spontaneously.

Prelabour rupture of membranes (PROM): The amniotic sac has ruptured before the onset of labour.

Preterm prelabour rupture of membranes (P‑PROM): The amniotic sac has ruptured before the onset of labour and before 37 weeks gestation (preterm).

Prolonged rupture of membranes (also PROM): The amniotic sac ruptures more than 18 hours before delivery.

 

Prematurity

Prematurity is defined as birth before 37 weeks gestation. The more premature the baby, the worse the outcomes.

Babies are considered non-viable below 23 weeks gestation. Generally, from 23 to 24 weeks, resuscitation is not considered in babies that do not show signs of life. Babies born at 23 weeks have around a 10% chance of survival. From 24 weeks onwards, there is an increased chance of survival, and full resuscitation is offered.

The World Health Organisation classify prematurity as:

  • Under 28 weeks: extreme preterm
  • 28 – 32 weeks: very preterm
  • 32 – 37 weeks: moderate to late preterm

 

Prophylaxis of Preterm Labour

Vaginal Progesterone

Progesterone can be given vaginally via gel or pessary as prophylaxis for preterm labour. Progesterone has a role in maintaining pregnancy and preventing labour by decreasing activity of the myometrium and preventing the cervix remodelling in preparation for delivery. This is offered to women with a cervical length less than 25mm on vaginal ultrasound between 16 and 24 weeks gestation.

 

Cervical Cerclage

Cervical cerclage involves putting a stitch in the cervix to add support and keep it closed. This involves a spinal or general anaesthetic. The stitch is removed when the woman goes into labour or reaches term.

Cervical cerclage is offered to women with a cervical length less than 25mm on vaginal ultrasound between 16 and 24 weeks gestation, who have had a previous premature birth or cervical trauma (e.g. colposcopy and cone biopsy).

Rescue” cervical cerclage may also be offered between 16 and 27 + 6 weeks when there is cervical dilatation without rupture of membranes, to prevent progression and premature delivery.

 

Preterm Prelabour Rupture of Membranes

Preterm prelabour rupture of membranes is where the amniotic sac ruptures, releasing amniotic fluid, before the onset of labour and in a preterm pregnancy (under 37 weeks gestation).

 

Diagnosis

Rupture of membranes can be diagnosed by speculum examination revealing pooling of amniotic fluid in the vagina. No tests are required.

Where there is doubt about the diagnosis, tests can be performed:

  • Insulin-like growth factor-binding protein-1 (IGFBP-1) is a protein present in high concentrations in amniotic fluid, which can be tested on vaginal fluid if there is doubt about rupture of membranes
  • Placental alpha-microglobin-1 (PAMG-1) is a similar alternative to IGFBP-1

 

Management

Prophylactic antibiotics should be given to prevent the development of chorioamnionitis. The NICE guidelines (2019) recommend erythromycin 250mg four times daily for ten days, or until labour is established if within ten days.

Induction of labour may be offered from 34 weeks to initiate the onset of labour.

 

Preterm Labour with Intact Membranes

Preterm labour with intact membranes involves regular painful contraction and cervical dilatation, without rupture of the amniotic sac.

 

Diagnosis

Clinical assessment includes a speculum examination to assess for cervical dilatation. The NICE guidelines (2017) recommend:

  • Less than 30 weeks gestation, clinical assessment alone is enough to offer management of preterm labour.
  • More than 30 weeks gestation, a transvaginal ultrasound can be used to assess the cervical length. When the cervical length on ultrasound is less than 15mm, management of preterm labour can be offered. A cervical length of more than 15mm indicates preterm labour is unlikely.

 

Fetal fibronectin is an alternative test to vaginal ultrasound. Fetal fibronectin is the “glue” between the chorion and the uterus, and is found in the vagina during labour. A result of less than 50 ng/ml is considered negative, and indicates that preterm labour is unlikely.

 

Management

There are several options for improving the outcomes in preterm labour:

  • Fetal monitoring (CTG or intermittent auscultation)
  • Tocolysis with nifedipine: nifedipine is a calcium channel blocker that suppresses labour
  • Maternal corticosteroids: can be offered before 35 weeks gestation to reduce neonatal morbidity and mortality
  • IV magnesium sulphate: can be given before 34 weeks gestation and helps protect the baby’s brain
  • Delayed cord clamping or cord milking: can increase the circulating blood volume and haemoglobin in the baby at birth

 

Tocolysis

Tocolysis involves using medications to stop uterine contractions. Nifedipine, a calcium channel blocker, is the medication of choice for tocolysis. Atosiban is an oxytocin receptor antagonist that can be used as an alternative when nifedipine is contraindicated.

Tocolysis can be used between 24 and 33 + 6 weeks gestation in preterm labour to delay delivery and buy time for further fetal development, administration of maternal steroids or transfer to a more specialist unit (e.g. with a neonatal ICU). It is only used as a short term measure (i.e. less than 48 hours).

 

Antenatal Steroids

Giving the mother corticosteroids helps to develop the fetal lungs and reduce respiratory distress syndrome after delivery. They are used in women with suspected preterm labour of babies less than 36 weeks gestation.

An example regime would be two doses of intramuscular betamethasone, 24 hours apart.

 

Magnesium Sulfate

Giving the mother IV magnesium sulfate helps protect the fetal brain during premature delivery. It reduces the risk and severity of cerebral palsy. Magnesium sulphate is given within 24 hours of delivery of preterm babies of less than 34 weeks gestation. It is given as a bolus, followed by an infusion for up to 24 hours or until birth.

Mothers need close monitoring for magnesium toxicity at least four hourly. This involves close monitoring of observations, as well as tendon reflexes (usually patella reflex). Key signs of toxicity are:

  • Reduced respiratory rate
    Reduced blood pressure
  • Absent reflexes

 

Last updated September 2020
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