Background: Gravida's poor periodontal health is emerging as a modifiable independent risk factor for preterm delivery and low birth weight. Methods: To test the hypothesis that oral bacteria other than periodontal pathogens are also associated with pregnancy outcomes, specific oral bacterial levels measured during pregnancy were evaluated in relation to gestational age and birth weight while controlling for demographic, medical, and dental variables. The study population consisted of 297 predominantly African-American women who were pregnant for the first time. The salivary bacterial levels evaluated were Streptococcus mutans, Streptococcus sobrinus, Streptococcus sanguinus, Lactobacillus acidophilus, Lactobacillus casei, Actinomyces naeslundii geno-species (gsp) 1 and 2, total streptococci, and total cultivable organisms. Results: For 1 unit increase in log10 A. naeslundii gsp 2 levels, there was a 60 gm decrease in birth weight (β = -59.7 g; SE = 29.1; P = 0.04), and a 0.17 week decrease in gestational age (β = -0.17 wk; SE = 0.09; P = 0.05). In contrast, per 1 unit increase in log10 L. casei levels, there was a 42 gm increase in birth weight (β = 42.2 g; SE = 19.3; P = 0.03), and a 0.13 week increase in gestational age (β = 0.13 week; SE = 0.06; P = 0.04). Conclusions: We conclude that other oral bacterial species can also be related to pregnancy outcomes in addition to previously reported periodontal pathogens. These organism levels may not only predict poor pregnancy outcomes, but also be used as modifiable risk factors in reducing prematurity and low birth weight.