Epidemiology and Etiology of Preterm Birth and Low Birth Weight

While treating gingivitis in pregnant women is of concern for optimal oral health, there is evidence gingivitis may influence pregnancy outcomes, which makes intervention of interest from a public health standpoint and gives further weight to effecting a cure.25,26 Periodontal disease has been identified as a risk factor for adverse pregnancy outcome,27,28 but the efficacy of periodontal treatment on birth outcomes has been inconsistent.25,26,29-32 

Preterm birth is defined as those deliveries that occur at less than 37 weeks of gestational age and account for 75% of perinatal mortality and half of the long-term morbidity.33 The overall rate of preterm birth in the United States was 9.4% in 2014  (Figure 1).7 Additionally, preterm birth rates among ethnic minorities  demonstrate a wide disparity in maternity outcomes with Black and Native Americans having the highest preterm birth rates at 13.4% and 10.4%, respectively.7 Only four states in the U.S. (Washington, Oregon, Idaho, and Vermont) achieved rates of preterm birth in 2014 at or below the March of Dimes target of 8.1%.7 

Figure 1. National Natality Statistics By State in 2014.7
national-natality-stats

Preterm birth may be due to (1) medical indication for maternal or fetal health, (2) spontaneous preterm labor with intact membranes, or (3) preterm premature rupture of the membranes (PPROM).34 Approximately 30-35% of preterm births are indicated, 40-45% follow spontaneous preterm labor, and 25-30% occur after PPROM.34 About 5% of preterm births occur at less than 28 weeks of gestation (extreme prematurity), about 20% at 32-33 weeks of gestation (moderate prematurity) and 60-70% occur after 34 weeks of gestation (late prematurity). Increasingly early prematurity is also associated with higher rates of morbidity and mortality.34

Preterm labor is thought to be initiated by myriad mechanisms including infection or inflammation, uteroplacental ischemia or hemorrhage, uterine overdistension, stress, maternal risk factors, and other immunologically mediated processes.35 Most cases of preterm birth are unexplained, but it has been postulated that many of these cases are mediated by immunoinflammatory processes including periodontal inflammation.36 It is critical to identify at-risk individuals for preterm birth so interventions can be targeted at the most vulnerable populations to reap the most benefits.37