Low Birth-Weight Babies
M. Stefanak, T. Styka, J. Warga
Low birth weight (less than 2,500 grams or 5.5 pounds) is a significant contributor to health and developmental problems and deaths among infants. An important risk factor for low birth weight is cigarette smoking during pregnancy, which has also been linked to an increased risk of preterm (premature) delivery.
Fewer new mothers in Mahoning County reported smoking cigarettes while they were pregnant in 1996, continuing the downward trend in smoking prevalence observed during the 1990's (Figure 1). Although the 20.0 percent smoking prevalence rate (reported on birth certificates) in 1996 represents a 23 percent reduction in cigarette smoking since 1991, it is unlikely that Mahoning County will achieve the Healthy People 2000 objective of no more than 10 percent smoking prevalence during pregnancy by 2000.
Using the information available from 1996 birth certificates, we were able to estimate the proportion of low birth-weight deliveries that are attributable to cigarette smoking during pregnancy. Among 613 Mahoning County residents who reported smoking cigarettes during pregnancy in 1996 the rate of low birth-weight deliveries was 12.4 percent. Among nonsmokers, this rate was 7.2 percent. Women who smoked during pregnancy were 1.8 times more likely to deliver a low birth-weight baby (Table 1).
| Table 1 | |||||
| Smoking and Low Birth-Weight Births, 1996 | |||||
| Mahoning County Births | 3,087* | ||||
| Births to Smokers | 616# | ||||
| Low Birth Weight (LBW) Births | 254 | 20.00% | |||
| LBW Births to Smokers | 76 | 8.30% | |||
| Odds Ratio for LBW | 1.8 (95% CI = 1.4, 2.4) | ||||
| Attributable Proportion for LBW | 13.30% | ||||
| * 14 birth certificates were not coded for birth weight or tobacco use | |||||
| # three birth certificates reported tobacco use but not birth weight | |||||
The proportion of all low birth-weight deliveries attributed to cigarette smoking during pregnancy in 1996 was 13.3 percent. This means that about 34 of the 254 low birth-weight deliveries to Mahoning County residents in 1996 - almost one in six - were due to this entirely preventable risk factor.
Birth certificate information also enabled us to estimate the proportion of preterm deliveries (less than 36 weeks gestation) that was attributable to cigarette smoking during pregnancy. Among women who reported smoking during pregnancy in 1996, the rate of preterm delivery was 9.8 percent. Among nonsmokers, this rate was 9.0 percent. Women who reported smoking during pregnancy were 1.1 times more likely to deliver prematurely.
The proportion of all preterm deliveries in Mahoning County attributable to cigarette smoking in 1996 was 1.9 percent (Table 2). Although the effect of smoking on preterm delivery is much smaller than on low birth weight, the risk of preterm birth is increased by 10 percent in smoking mothers.
| Table 2 | |||||
| Cigarette Smoking and Preterm Births, 1996 | |||||
| Preterm Births | 282 | 9.2%* | |||
| Preterm Births to Smokers | 60 | ||||
| Odds Ratio | 1.1 (95% CI = 0.8, 1.5) | ||||
| Attributable Proportion | 1.90% | ||||
| * 21 birth certificates were not coded for gestational age or tobacco use; | |||||
| seven reported tobacco use but not gestational age | |||||
In this analysis we have highlighted the large effect of maternal cigarette smoking on pregnancy outcomes in Mahoning County. Smoking may be the single most important preventable risk factor for low birth weight. Community organizations promoting early and adequate prenatal care should insist that preconceptual education about smoking risks and prenatal smoking cessation counseling and support are universal components of quality perinatal health services.
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