Tutorial 8: Pre-term Birth

Question 1

What is Preterm birth?

Answer 1

“Preterm” is defined as the birth of a baby less than 37 weeks completed gestational age. The rate of incidence is between 5-10% in most developed countries.

Question 2

Are most pre-term births spontaneous or iatrogenic?

Answer 2

Spontaneous preterm births (preterm labour/ PROM premature rupture of the membranes) make up about 65-75% of all preterm births, whereas iatrogenic contributions (i.e., for a maternal or foetal indication) are around 25-35%.

Question 3

Why is preterm birth of importance?

Answer 3

Preterm birth is a major cause of neonatal morbidity and mortality, and results in 75-90% of all neonatal deaths; those not due to lethal congenital malformations.

At gestations under 26 weeks, overt neurological damage occurs in about 1 in 4 babies, resulting in morbidities such as cerebral palsy, blindness, or deafness.

Question 4

What are some risk factors for spontaneous preterm birth?

Answer 4

1. Age <18 or >35
2. Previous preterm birth – one previous case increases risk 4 fold, 2 cases increases risk 6.5 fold.
3. Infections – e.g. UTI
4. Multiple pregnancies
5. Maternal BMI <18, >30
6. Maternal High Blood Pressure, Diabetes
7. Bleeding in pregnancy – APH, threatened miscarriage
8. Cervical compromise (short/cervical surgeries such as cone biopsy, radical diathermy)
9. Pregnancy Interval (<6months)
10. Previous surgical terminations
11. Periodontal disease
12. Lifestyle factors: Smoking, Alcohol, other drugs
13. Ethnicity
14. Marital status! (Increased in unmarried mothers)

Question 5

What is the MoA of preterm birth?

Answer 5

Exact cause not known, but likely to be multifactorial. The most important ones that have been identified are –

1. Precocious foetal endocrine activation
2. Uterine over distension (placental abruption, multiple pregnancies)
3. Bleeding
4. Intrauterine inflammation/infection – UTI

Question 6

What parts of the Hx and Ex would you include for a woman with suspected preterm labour?

Answer 6

History:

• Contractions – frequency, strength (discomfort vs painful), length
• Show
• Preterm prelabour rupture of membranes (PPROM)
• Backache
• Identify risk factors, especially previous preterm birth, infections, cervical trauma and multiple pregnancies.

Examination:

• Palpate abdomen for contractions, fetal lie, presentation and engagement
• Speculum examination – blood, liquor pooling, cervix effacement and dilatation.

Question 7

Wha investigations would you perform for a woman with suspected preterm labour?

Answer 7

1. Fetal fibronectin: Fetal fibronectin “leaks” into the vagina if a preterm delivery is likely to occur.
2. Cardiotocogram – establish well-being of foetus and maternal contractions.
3. Cervical length on transvaginal USS (<2cm)
4. Bloods (FBC, CRP), Urine dipstick/MSU, High vaginal swabs (screen for group B streptococcus)

Question 8

What is the role of the Fetal Fibronectin test in woman with suspected preterm labour?

Answer 8

Foetal fibronectin is a protein produced by foetal cells and is found at the interface of the chorion and decidua. It serves to function as “biological glue” that binds the foetal sac to the uterine lining.

The protein is found in the vagina when the process of labour begins. Thus the diagnostic test looks for the presence of foetal fibronectin.

It has a very high negative predictive value and if negative, 99.5% of women will not give birth spontaneously in the next 7 days following the test. The positive predictive value is less useful with 13-30% of women giving birth in the next 7 days following a positive test.

The test itself requires a vaginal swab specimen which is then placed in a transport tube and sent to lab for testing. It is important to take the swab before performing a d_igital examination t_o reduce the numbers of false positives.

Question 9

What are some stratergies to prevent preterm labour before pregnancy?

Answer 9

1. Raising awareness of the issue and the major contribution it has towards infant mortality in the public and professional domains, in order to reduce avoidable risk factors. E.g.

• reducing the number of uterine instrumentation (repeated surgical abortions),
• adoption of specific professional policies such as only one embryo implant during IVF treatment to reduce multiple pregnancies.
• less invasive techniques for treating cervical intra-epithelial neoplasia

2. Smoking cessation – A Cochrane review reported that smoking cessation programmes in pregnancy successfully reduce the incidence of preterm birth.
3. ?Lifestyle factors – Avoidance of prolonged working hours (over 42/week) or night work. Avoidance of weight extremes.

Question 10

What are some stratergies to prevent preterm labour during pregnancy?

Answer 10

1. Screening for UTI in asymptomatic women followed by appropriate treatment to reduce rates of pyelonephritis and thus risk of preterm birth. On the other hand, routine screening for bacterial vaginosis is not recommended as treatment does not consistently improve outcome.
2. Progesterone promotes pregnancy and uterine quiescence. Prescription can be 100mg vaginally once a day until 34 weeks gestation.
3. Tocolytic agents may prolong gestation by between 2 to 7 days and are recommended for short-term use to provide time for administration of antenatal corticosteroids and transfer to an appropriate neonatal unit.
4. ?Cervical cerclage can be performed in those who have a singleton and have had a previous preterm birth as well as having a shortened cervix (<2.5cm) on an USS. This may help in reducing preterm birth rates in these women. More studies needed.

Question 11

What is the role of antenatal steroids in woman at risk of preterm birth?

Answer 11

Premature infants are not able to produce surfactant and thus have underdeveloped lungs which can lead to respiratory distress syndrome.

To improve the outcomes for the neonate in preterm birth, women at risk of delivering before 34 weeks are usually administered one course of glucocorticoids (e.g. betamethasone, dexamethasone), which cross the placental barrier and stimulate surfactant production in the foetus. Usually this administration only occurs after the foetus has reached viability at 23 weeks.

Question 12

What is the role of tocolysis in woman at risk of preterm birth?

Answer 12

Tocolysis is the process of prescribing medications (tocolytics) to supress premature labour/uterine contractions. The main benefit from this is to prolong gestation 2 to 7 days in order to provide time for administration of antenatal corticosteroids and transfer to an appropriate neonatal unit.

The drug most commonly used is Nifedipine. Contraindications to Nifedipine include cardiac disease.

Question 13

How does the management of preterm labour differ between a rural and a tertiary hospital?

Answer 13

Rural:

• less services available and thus it becomes more a matter of trying to prevent the pre-term birth. This would involve:
  
  • Managing maternal medical conditions
  • Weekly check-ups for those at high risk (checking symptoms as well as cervical dilatation).
  • Those who are suspected of entering pre-term labour could be held for monitoring and if it turns into established pre-term labour an immediate transfer to a tertiary care setting which has NICU services available should be done if possible.