Is Maternal Periodontal Disease a Risk Factor for Preterm Low Birth Weight Infants in New Zealand: A Pilot Study

Abstract

The prevention of preterm birth has been a focus of modern maternity care for many years. However, the frequency with which these births occur has not changed significantly during the past 40 years (Offenbacher, Lieff, Boggess, Murtha, Madianos & Champagne et al., 2001). The exact mechanism by which preterm birth is thought to occur remains poorly understood although systemic and localised infection remain well recognised risk factors. Maternal periodontal disease has recently received attention from the scientific community as several studies conducted in the United States of America and Europe have suggested that periodontal disease may be a potentially modifiable causative agent. Maternal periodontal disease has however received very little attention within New Zealand. This thesis describes the piloting of a prospective study, which was undertaken in order to examine the relationship between maternal periodontal disease and preterm low birth weight infants. The aim of the pilot study was to determine both the feasibility of undertaking a large-scale study and to identify the strengths and weaknesses within the research design. The plan was to recruit 60 otherwise healthy multiparous women who were due to give birth to a single infant in July or August 2005. Thirty women were to have been assigned to the comparison group if during this or a previous pregnancy they had given birth to an infant weighing more than 2500 grams and after 37 weeks gestation. The other 30 women were to have been assigned to the case group if during this or a previous pregnancy they had given birth to an infant weighing less than 2500 grams and prior to 36 completed weeks gestation. For this latter group of women the birth must have been preceded by either the spontaneous onset of preterm labour or preterm premature rupture of the membranes. At 28 weeks gestation each of the study participants had a sample of microbial tongue flora and dental plaque collected with a small nylon brush. Within 72 hours of the women giving birth, repeat microbial samples were collected. These samples were analysed by the Dental Research Group at the University of Otago using the checkerboard DNA:DNA hybridization technique. This technique was used in order to quantify the presence or absence of 40 different oral organisms that could be associated with the birth of a preterm low birth weight infant. A full mouth periodontal assessment was also performed by a qualified dentist within 72 hours of the women giving birth. At this assessment gingival bleeding and clinical attachment loss were measured and recorded at three sites per tooth. Fifty eight multiparous women were recruited to participate in the study which was undertaken in a tertiary level hospital within New Zealand. No relationship was identified between maternal periodontal disease and preterm low birth weight infants. However this is not surprising given the limited size and scope of the pilot study population. The only way to clearly establish whether maternal periodontal disease and preterm low birth weight infants are truly linked is to undertake the proposed large-scale study. This pilot study identified several areas where the proposed large-scale study would have encountered significant problems. The inability of this pilot study to recruit sufficient numbers of eligible 'case' women is in itself an issue. The timing of any future study must also be carefully considered because the number of maternity care providers within New Zealand is limited. When women were invited to participate in this study several midwives who were approached were already engaged in recruiting women for a different study. Therefore it is important to ensure that two large-scale studies do not attempt to recruit pregnant women from the same study facility simultaneously. The number of women that will be required to participate in the proposed largescale study also requires careful consideration because sufficient numbers of women must be recruited to both the case and the comparison groups to ensure that statistical power is achieved. A comparison of the microbial tongue flora and dental plaque samples has now confirmed that only the dental plaque samples were discriminatory. Therefore in any future study only the latter samples should be collected. Many of the project management issues that were identified during the pilot study phase can now be more appropriately addressed thus ensuring a robust study design with valid and reliable measures.