Background:
Both preterm births (PB) and sexually transmitted diseases during pregnancy (STD/P) increased from 1997 to 2004 in Louisiana. PB was 11.6% in 1997 and 13.3% in 2004. STD/P was 3.3% in 1997 and 6.0% in 2004.

Objective:
To define relationship between STD/P and PB.

Method:
1999-2004 STD/2000-2004 birth records linked data was analyzed. STD/P included only chlamydia, gonorrhea, and syphilis in this study. Univariable and multivariable logistic regression in SAS 9.0 was used to define relationships between STD/P and PB, adjusting mothers' race, education, age, marital status, smoking, medical risks, geographic area and prenatal care entry.

Result:
PB in mothers who were not infected by any STD/P was 12.5% and in those who were infected by chlamydia, gonorrhea, and syphilis it was 14.6 %, 17.7%, and 19.7% respectively. Unadjusted and adjusted odds ratios (OR) of PB for chlamydia were 1.2 (CI: 1.1-1.3) and 1.0 (CI: .9-1.0), for gonorrhea 1.5 (CI: 1.4-1.7) and 1.2 (CI: 1.1-1.3), and for syphilis 1.7 (CI: 1.2-2.3) and 1.3 (CI: 0.9-1.8). Women who were black, unmarried, greater or equal 35 years old, smokers, less educated, had no or late prenatal care, and had medical risks were statistically significant to have increased PB.

Conclusion:
Pregnant women who were infected by gonorrhea were 20% more likely to have PB than those who were not infected any STD/P. The multivariable logistic regression model did not show statistical relationships between PB and chlamydia as well as syphilis.

Implications:
Early and appropriate treatment might reduce affects of chlamydia and syphilis on PB. Further studies of STD/P related to other maternal and child morbidities and mortalities should be conducted.