Causes of Low Birth Weight

In Ottawa the Low Birth weight (LBW) rate was 4.2% in 2002. Information from the Niday Perinatal Database suggests that this rate changed very little from the previous three years. The two main causes of LBW are early delivery, also known as preterm birth, and poor fetal growth.


Preterm Birth

About 70% of all LBW babies are born preterm - before 37 completed weeks of pregnancy. Some of the risk factors for preterm birth are:

  • Carrying more than one baby such as twins or triplets
  • Previous preterm birth
  • Smoking or exposure to second hand smoke
  • Stress and lack of support
  • Infection- some infections in pregnant women, such as bladder or vaginal infections, can cause labour to start early
  • Stressful work conditions such as
    • Long hours
    • Being on your feet for long periods
    • Exposure to harmful substances
  • Previous abortions
Carson was born at 25 weeks gestation. He was 13 inches long and weighed 1lb. 14 ozs. (900 grams) Here he is 4 weeks old and wearing his parents wedding bands on his wee foot. He is a healthy 22-month old today, although asthmatic, and now has his parents wound around his finger.  


Some signs and symptoms of preterm labour
These signs are important especially if they are new or different:
  • A sudden gush or a constant slow leak of fluid from the vagina
  • Bleeding from the vagina
  • Contractions of the uterus
Or a change in what you normally feel in:
  • Low dull backache
  • Pelvic pressure (feeling full or heavy 'down below')
  • Discharge from the vagina
Some women may just feel that "something is not right"
Source: "Preterm Labour - It Might Happen to You"

The following links provide excellent information on preterm labour and/or delivery:
Best Start:
City of Ottawa: Women's Health


Poor Fetal Growth:

The remaining 30% of low birth weight babies are born at full term, but did not grow properly in the womb. Some reasons for this may be:

  • Smoking - women who smoke are 2-3 times more likely to have a LBW baby
  • Exposure to second hand smoke can also contribute to LBW
  • Stress
  • Abuse and /or family violence
  • Living in poverty
  • Poor nutrition - women who do not gain at least 10 kg (22lb) are 2-3 times more likely to have a LBW baby
  • Being under weight before becoming pregnant
  • Mothers age at time of pregnancy - women under 20 and over 45 are more likely to have a LBW baby.
  • Lack of social support
  • Exhaustion or lack of rest
  • Use of alcohol & drugs - for more information on the effects of alcohol on pregnancy, please visit:

Fortunately, there are things that can be done to prevent low birth weight. For that reason it is everyone's responsibility to understand LBW, its causes and simple things that can be done to decrease the chance of it happening.


  • Best Start (1998). Prevention of Low Birth Weight in Canada: Literature Review and Strategies (2nd ed.).
  • Best Start (2002). Preterm Birth: Making a Difference. Collaborative project of Best Start, PPPESO, SOGC


The incidence of disability among low birth weight babies is low.
True  |  False more questions
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