Clean Teeth Do Not Prevent Preterm Birth

MINNEAPOLIS, Nov. 2 -- Treating periodontal disease during pregnancy does not lessen the likelihood of preterm birth, according to researchers here.

A randomized study of 823 pregnant primarily low-income women with periodontitis found that treatment is safe during pregnancy, but that good periodontal hygiene has no significant bearing on preterm births, reported Bryan S. Michalowicz, D.D.S., of the University of Minnesota, and colleagues, in the Nov. 2 issue of the New England Journal of Medicine.

Periodontal cleaning and plaque removal (scaling and root planing) during pregnancy did not significantly improve rates of preterm birth, low birth weight, or fetal growth restriction compared with putting off treatment until after pregnancy, the investigators found.

These findings run counter to results of several small studies that have suggested such associations, and the relative ease of periodontal intervention made this an attractive hypothesis as a way to reduce preterm deliveries, said an accompanying editorial by Robert L. Goldenberg, M.D., and Jennifer F. Culhane, Ph.D., both of Drexel University in Philadelphia.

In the trial, the 823 women with periodontitis were randomized to standard non-surgical treatment before 21 weeks gestation or after delivery.

Periodontitis was diagnosed as at least four teeth with at least 2 mm loss of attachment of the gums to the teeth and at least 4 mm depth measured using a dental probe, as well as bleeding at the site of 35% or more of probe measurements.

The women had to be at least 16 years old and be at 13 to 17 weeks of gestation at baseline. Both groups received monthly oral examinations, but only those in the treatment group underwent periodontal scaling and root planing in addition to monthly tooth polishing.

There were few outcome differences between the during-pregnancy and delayed treatment groups. The researchers found:

• A similar rate for the primary outcome measure, preterm birth defined as before 37 weeks of gestation (12.0% versus 12.8%, hazard ratio between groups 0.93, 95% confidence interval 0.63 to 1.37, P=0.70),
• No significant difference in birth weight (3,239 g versus 3,258 grams, P=0.64),
• Nearly equal rates of small-for-gestational age births (12.7% versus 12.3%, odds ratio 1.04, 95% CI 0.68 to 1.58),
• No significant difference in the rate of spontaneous abortions (loss before 20 weeks) or stillbirths (5 versus 14 control, P=0.08) and
• No significant difference in any of the secondary outcomes, including preeclampsia.

Since the 95% confidence interval of the hazard ratio for preterm delivery between groups crossed one, the researchers said they "cannot rule out a modest increase or decrease in the risk of preterm delivery with periodontal treatment."

The nonsignificant reduction in spontaneous abortion or stillbirth with periodontal treatment should be viewed "with particular caution" because only 19 patients met this secondary outcome. The results were unchanged when spontaneous abortions were excluded or when the 19 deliveries that had to be induced for medical reasons before 37 weeks of gestation were treated as lost to follow-up.

For many of the patients, the study pregnancy was not their first. Of these 531 women, 14.5% had a previous live preterm birth. During their study pregnancy, some women also had other risk factors including urinary tract infections (22%), bacterial vaginosis (12%), gestational diabetes (6%), group B streptococcal colonization (16%), and tobacco use (13%). However, these factors did not differ significantly between groups.

The periodontal cleaning and treatment improved all clinical measures of disease, the researchers said.

It also appeared to be safe. There was not a significant difference in the number of serious medical adverse events between groups, including hospitalization for any reason, congenital anomaly in the baby, spontaneous abortion, stillbirth, or neonatal death (9.0% treatment group versus 10% control group, P=0.64).

Analyses limited to women with the most severe periodontal disease showed similar lack of significant difference between groups in preterm delivery risk.

Drs. Goldenberg and Culhane suggested two explanations for the study's negative findings. "Periodontal disease may not be in the causal pathway to preterm birth, and even if it is, treatment of periodontal disease during pregnancy simply may not reduce the rate of preterm birth."

They suggested that "it is possible that treatment either before pregnancy (in nulliparous women) or in the period between pregnancies (for multiparous women, especially those with a history of preterm birth) may yield more promising results."