Please note: In 2003, the CTF updated its Grades of Recommendations to include an "I Recommendation" for situations where insufficient evidence exists to allow a recommendation to be made.  (Formerly, these situations were captured under a "C Recommendation".)  This change is not retroactive, and all "C Recommendations" made prior to 2003 have not been reevaluated in light of the new "I" recommendation grade.  For a discussion of these recommendation grades, please link to the 2003 article in the Canadian Medical Association Journal here.

Prepared by Orlando P. da Silva, MD, FRCPC Department of Pediatrics, Division of Neonatology, The University of Western Ontario

Objective
To make recommendations for prevention of low birth weight (LBW) or preterm birth in high-risk or low-risk pregnant Canadian women.

Burden of Suffering
LBW is associated with about 75% of early neonatal mortality in both Canada and the U.S.  A U.S. study found that 83% of deaths were associated with delivery <37 weeks and 66% with delivery <29 weeks.  About 6% of infants born in Canada are of LBW.  The average cost per admission in the U.S. has been estimated to be over US$7,500 per infant, not including long-term care.  In developed countries, cigarette smoking is the most important established factor with a direct causal impact on the rate of intrauterine growth retardation (defined as birth weight <2,500 g and gestational age >37 weeks).  Other important factors include poor gestational nutrition, low pre-pregnancy weight, primiparity, female sex and short stature.  Smoking, prior preterm delivery, spontaneous abortion and low pre-pregnancy weight seem to play an important role in determining the rate of preterm births.

Options
Multicomponent programs can include education; advice on working, smoking, stress, usual activities, sexual practices, nutrition, and bed rest; self monitoring of uterine activity; antenatal care, external support systems, and specific obstetrical practices (regular cervical examinations, cervical sutures, bed rest in the hospital, progestgens, -mimetics, and calcium antagonists).

Outcomes
Infant mortality, birth weight and morbidity, preterm labour and delivery, and nutritional status.

Evidence
The Cochrane Collaboration Database on Pregnancy and Childbirth and MEDLINE (1966 to January 1994) were searched using the terms low birth weight, prematurity and prevention. Experts were also contacted. Study results were synthesized in table or graphic format only.

Values
The 13-member Task Force of experts in family medicine, geriatric medicine, pediatrics, psychiatry and epidemiology used an evidence-based method for evaluating the effectiveness of preventive health care interventions. Recommendations were not based on cost-effectiveness of options. Patient preferences were not discussed.

Background papers providing critical appraisal of the evidence and tentative recommendations prepared by the chapter author were pre-circulated to the members. Evidence for this topic was presented and deliberated upon in 1- to 2-day meetings, 2 to 3 times per year from January 1993 1992 to April 1994. Consensus was reached on final recommendations.

Benefits, Harms, and Costs
Multicomponent programs have shown mixed results in high-risk and low-risk pregnancies although before and after studies have shown reductions in preterm deliveries from 5% to 7% before the program to 2% to 6% after the program. However, these studies have significant methodological limitations.  6 RCTs and 1 nonRCT showed conflicting results and positive results only in subgroup or regression analyses that account for baseline differences.

RCTs and meta-analyses have not shown improvements in rates of pre-eclampsia or neonatal outcomes for women with pregnancy-induced high blood pressure who take low-dose aspirin.

Social support programs have been evaluated in 4 RCTs and 1 meta-analysis of 8 studies. The evidence is consistent in showing that social support alone is not effective in overriding the cumulative effects of social and biologic disadvantage.

Nutritional supplementation has been evaluated in a series of programs (Nutritional Supplementation Programs for Women, Infants, and Children). The programs decreased low and very low birth delivery by 1% to 2% and increased birth weight from 0 to 60 g, and had better outcomes and costs (for every $1 spent on the program the savings in medical care were $2.91).   The wide range of benefit shown in different studies can be attributed to differences in the populations studied, in the supplements used, and in methodological quality of the study design, and the clinical significance of this difference is unclear.  A Canadian program and a meta-analysis showed similar results for birth weight and preterm delivery.

Recommendations
Recommendation grade [A, B, C, D, E]  and level of evidence [I, II-1, II-2, II-3, III] are indicated after each recommendation. Citations in support of individual recommendations are identified in the guideline text.

• There is inconclusive evidence that multicomponent education programs to prevent preterm delivery of low birth weight infants are effective for women with low-risk pregnancies [C, II-3] or high-risk pregnancies  [C, I].
• There is fair evidence that programs of social support alone for women with high-risk pregnancies do not prevent preterm birth [D, I].
• For women who are at high risk for undernutrition, there is inconclusive evidence regarding diet supplementation programs in the prenatal period to prevent low birth weight babies [C, I, II-2].

Sponsors
The Canadian Task Force on Preventive Health Care developed this guideline with funding from Health Canada.

Source Document
da Silva O.P. Prevention of low birth weight/preterm birth. In: Canadian Task Force on the Periodic Health Examination. Canadian Guide to Clinical Preventive Health Care. Ottawa: Health Canada, 1994; 38-50.