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Preterm Labour | Preterm Birth

Most babies are delivered between 37-41 weeks gestation and are considered to be at “term”.

Babies born before 37 weeks are considered to be “preterm” or “premature”. Babies born at 32-36 weeks are referred to as being “moderately or slightly” premature, those born before 32 weeks as being “very” premature and those born before 25 weeks as being “extremely” premature.

Depending on how early a baby is born, they may be at risk of a number of serious health problems or even death. The earlier their birth occurs, the greater are those risks.

Essential Information

  • In Canada, approximately 8% of babies (approximately 25,000) are born prematurely (< 37 weeks) every year.
  • Most premature babies do very well, but some, especially those who are born very early, may experience life-long challenges such as developmental delay, learning disability, physical handicap, lung or gastrointestinal problems, vision or hearing loss.
  • Women who have given birth prematurely in a previous pregnancy and/or who have certain risk factors are at a higher risk of giving birth prematurely. Their future pregnancies will need to be monitored closely.
  • Preterm babies may have to stay in the Neonatal Intensive Care Unit (NICU) for a prolonged period of time. Our NICU at Mount Sinai Hospital has experienced staff and specialized equipment to help deal with the many of the challenges that premature birth poses: e.g. breathing, keeping warm, feeding etc.
  • Mount Sinai Hospital is a prominent member of the Canadian Preterm Birth Network, the aim of which is to improve the outcomes for preterm infants and their families


Preterm birth is defined as a baby is born before 37 completed weeks of gestation.

Preterm birth is classified into two categories. One third of preterm births are “iatrogenic”, which means that there are medical reasons to plan an early delivery for the safety of the mother and/or her baby

Two thirds of preterm births are “spontaneous”, meaning that they were unplanned, unpredictable and unable to be stopped once the process started. This type of delivery can be defined as:

  • Preterm labour (contractions and cervical dilation)
  • Preterm rupture of the membranes (PPROM) (the amniotic sac breaks and amniotic fluid leaks out, triggering preterm labour or initiating other processes which may predispose to preterm birth)
  • Cervical insufficiency (the cervix dilates without contractions or PPROM).

Predicting that a woman is at a higher risk of preterm birth depends on the assessment of her risk factors including:

  • Past medical & social history
  • History of one or more preterm births
  • Multiple pregnancies (i.e. twins etc.)
  • Previous surgery on the cervix
  • Shortened cervical length
    • Cervical length is usually measured at the time of an anatomy ultrasound (~20 weeks), but maybe evaluated sooner and/or more frequently if there are additional risk factors and/or a previous preterm birth.

Treatment/Prevention of Preterm Birth

Women who are at risk of giving birth prematurely may be referred to our Prevention of Preterm Birth Clinic or Placenta Clinic, depending on their risk factor(s) for preterm birth. The goal of these clinics is to care for patients so that they can carry their pregnancy as far as it is safe to do so. Care is tailored to the specific needs of the patient and her family, taking into account her risk factors for giving birth early.

Caregivers in our clinic include doctors (obstetricians/maternal-fetal-medicine specialists & paediatricians), nurses, sonographers, social workers, nutritionists and perinatal psychiatric counselors/physicians.

Many approaches may help to promote a healthy pregnancy and to minimize the risk of preterm birth, including:

  • Optimizing maternal health & weight
  • Following a healthy lifestyle, without drug or alcohol abuse
  • Ensuring good nutrition
  • Zinc/Calcium supplementation
  • Omega 3 or pro-biotic supplementation
  • Smoking cessation
  • Maintaining good dental hygiene

Specific strategies for preterm birth prevention may be suggested based on risk factors, pregnancy history and ongoing pregnancy assessment, including:  

  • Screening for and treating vaginal and/or urinary tract infections
  • Progesterone supplementation (vaginal)
  • Cervical cerclage (a stitch inserted to reinforce the mechanical strength of the cervix)
  • Low dose aspirin.
  • Restricting vigorous activity

Referral Information

All patients at risk for preterm birth should be referred to a tertiary care centre, such as Mount Sinai Hospital for evaluation.