What is preterm birth?

Preterm is the birth that happens before 37 weeks of gestation. It is considered one of the most serious pregnancy complications. Most babies are born earlier because of spontaneous onset of labour. However, 1 in 4 babies are born premature due to medical intervention because either the mother or the fetus presents a complication (iatrogenic prematurity).

What are the consequences of having a preterm baby?

A preterm baby has increased risks of breathing and feeding difficulties and also increased risk for infections.

What causes preterm birth?

In the majority of cases the cause of preterm birth is unknown. Usually, mainly factors are implicated. Infection however, is one of the most important causes of preterm birth.

Woman who gave birth premature are at increased risk of preterm birth in their next pregnancy.

Increased risk for preterm birth

The risk of preterm birth increases in the following situations:

  • Premature rupture of membranes
  • Past history of preterm birth or premature rupture of membranes before 37 weeks of gestation
  • History of 2nd trimester miscarriage in past pregnancy
  • Vaginal bleeding after 14 weeks of gestation
  • Congenital uterine anomaly (i.e. bicornuate uterus)
  • Multiple pregnancy
  • Increased amniotic fluid
  • Smoking
  • History of cervical surgery (i.e. loop excision)
  • IVF conception
  • Maternal infections such as pyelonephritis or vaginal infection by Gardnerella Vaginalis

Interventions for prevention of preterm birth and its sequelae

The most important interventions are:

  • Antenatal corticosteroid therapy
    For women at increased risk for preterm birth is recommended the antenatal use of corticosteroid therapy in order to stimulate fetal lung maturation. The therapy is more effective when it is given within 7 days before birth.
  • Measurement of the cervical length
    The cervix is the lowest part of the uterus and remains long and closed during pregnancy. If it is too short or if it opens prematurely, there is increased chance of preterm birth.The measurement of the cervical length should be done with transvaginal ultrasound performed by trained doctors. Dr Tsoumpou trained at the Harris Birthright Centre of Fetal Medicine at King’s College Hospital London and she is certified by the Fetal Medicine Foundation for the assessment of the uterine cervix and for estimation of preterm birth risk.

    The test is performed at the 1st trimester during the nuchal scan and also at the fetal anatomy scan at 21-24 weeks of gestation. Depending on the individual history it might also need to be performed in the between i.e. at 16-18 weeks of gestation.

  • The measurement of cervical length is indicated in women with: 
    • History of preterm birth or of premature rupture of membranes in previous pregnancy
    • History of cervical incompetence
    • History of cervical surgery e. loop excision
    • Congenital uterine anomaly i.e. bicornuate uterus
    • Even women considered as low-risk might benefit from the examination of the cervix 
  • Infection prevention
    Frequent urine check for asymptomatic bacteriuria and vaginal culture for infection are important in preterm birth prevention, especially in women with a history of preterm birth or premature rupture of membranes in a previous pregnancy.

Therapeutic methods to reduce the risk of preterm birth

  • Vaginal progesterone
    The use of vaginal progesterone reduces by 45% the risk of spontaneous preterm birth before 34 weeks of gestation. Progesterone relaxes the uterus and prevents the migration of microbes from the vaginal to the uterine cavity by thickening the cervical mucus.
  • Arabin pessary
    The Arabin ring pessary is made from synthetic material and aims to correct the angle of a short cervix. A study published in the Lancet in 2012 showed that when it is used in women with cervical length >25 mm at the 2nd trimester anatomy scan reduces the chance of preterm delivery.
  • Cervical cerclage
    The cervical cerclage is indicated in women with history of cervical incompetence or with a very short cervix. The suture is removed after 37 weeks of pregnancy so that the woman could deliver vaginally.
  • Treatment of asymptomatic bacteriuria and Gardnerella vaginalis infection

For more information you could visit the following websites: