Study design and setting
A case-control study was conducted to ascertain the predictability of periodontitis with premature birth. Participants were selected through hospital registers whereby research team would verify daily to see the cases for preterm deliveries and the controls would be the next 2 on the register. The sample was calculated using G-Power 3.1.9.6. The researcher used small effect size of 0.06, alpha of 0.05 and power of 0.95 with 10 predictors. The G-Power calculation gave the sample size of cases of 185 and since the ratio was 1:2, then the controls were 370 and the total sample size was 555. The study was conducted at 12 health facilities in the Southern Province of Rwanda from February to August 2018.The study was done in the Southern Province of Rwanda in 6 districts, including Kamonyi, Muhanga, Ruhango, Nyanza, Huye and Gisagara. Corresponding district hospitals and nearby health centers were selected for the study and one referral hospital in Huye.
Data sources and measurement
A structured clinical exam and standardized questionnaire were used to collect information regarding the presence of periodontal infection among pregnant women attending antenatal care clinics in the Southern Province of Rwanda. The study adopted the questionnaire from the WHO Oral Health Assessment Tool for Adults of 2013 [20] to the Rwandan context. The questionnaire was sent to experts for content validation. It was piloted to ensure that it captures all variables and ensured that the questions were clear to the respondents.
The questionnaire was piloted in Nyamata District Hospital in the Eastern Province to ensure cross-cultural validation, and to ensure that it captures all the information required and clarity of questions. After the pilot study, all the inputs from the participants were considered and questions that were not clear were corrected accordingly. The questionnaire was translated in Kinyarwanda using forward and backward translation whereby this questionnaire was translated in Kinyarwanda from English and it was again translated back to English by another translator to see if the meaning remains the same and the corrections were harmonized.
The questionnaire assessed the following variables: age of the respondent, education level, health and lifestyle behavior e.g. Smoking, socio-economic status, mother’s weight, number of previous pregnancies, previous preterm and weight gain during pregnancy, illnesses during pregnancy and stress during pregnancy. The outcome variable was premature birth and other mentioned variables are independent variables.
Data collection procedures
A periodontal examination was performed on all women enrolled in the study. The study examiners used a calibrated William’s periodontal probe to perform the periodontal clinical examination. Six examiners were calibrated by a qualified dentist on how to perform a periodontal examination to see that they all understood it in the same way, to avoid having false results or different findings between patients.The calibration process focused on probe design, gentle and constant force of probing and proper angulations. While no formal agreement analysis was conducted, the examiners were required to examine at least 2 patients and oral examination was conducted until all examiners were in agreement with each other and with the trainer.The calibration results was considered valid only when there was no descripancy in results and when the results for 2 examiners were consistent. The examiners assessed bleeding on probing, probing depth and clinical attachment loss measured in mm at six different sites on each tooth (buccal-mesial, mid-buccal, buccal-distal, lingual-mesial, mid-lingual and lingual-distal). The mothers in the study group were asked about their dental care practices and their smoking habits. In addition, a full-mouth periodontal screening was done by the lead researcher with the calibrated dental therapists acting as research assistants. However, the research team were blind to the case and control.
The study subjects were examined at their bedsides by the researcher and calibrated research assistants using a periodontal probe, intraoral mirror and headlights. A gentle probing force was applied to guide the tip into the periodontal pocket until the resistance was felt. The pocket depth was measured using the gingival margin as a reference point.
Clinical attachment loss was measured as follows: when the gingival margin was at the cemento-enamel junction and there was no recession, then the CAL was equal to the pocket depth; when the gingival margin was apical to the cemento-enamel junction, CAL was equal to pocket depth plus gingival recession; when the gingival margin was on the anatomical crown in case of gingival overgrowth, CAL was equal to pocket depth minus gingival recession. CAL was not considered in some of the specific cases that were of non-periodontal cause. For example, when the gingival recession was of traumatic origin, dental caries extending in the cervical area of the tooth and in the cases of recession by malposition of the tooth [21].
The current study defined periodontitis as presence of pocket depth greater than 3 mm on either maxilla or mandible or both and presence of interdental clinical attachment loss (CAL) on ether maxilla, mandible or both of 2mm or above and buccal or oral CAL of 3 mm or above [21].
Based on Jati et al (2016), gingival recession was defined as “apical migration of marginal gingiva and characterized by gradual displacement of gingiva away from the cemento-enamel junction that results in the root surface exposure to the oral environment” [22]. The research team completed the exams and questionnaires with study subjects until the required sample was reached.
The current study defined some of the variables as follows; physical trauma as a wound on the body that was caused by a sudden physical injury, for example, an accident. Violence as any behavior or action that intends to hurt someone, physical or verbal and stress during pregnancy as anything that causes emotional strain or tension to the pregnant women.
Participants and Inclusion/exclusion criteria
The inclusion criteria were postpartum mothers aged 18-35 who delivered singleton infants within 1 to 5 days before recruitment in all selected health facilities. Those women who delivered premature were recuited as cases and those who delivered at term were recruited as controls. Maternal registers were checked in order to determine who could be recruited as case or controls based on the above criteria. Mothers with twin infants, those with systemic conditions like uncontrolled diabetes, HIV infection and those without teeth in one or more sextants were excluded from the study. Women whose conditions could obviously lead to prematurity like abnormal placentation, eclampsia, uterine abnormalities, and other pregnancy complications that may easily lead to prematurity were also excluded from the study so that they do not bias the results. Other variables that were likely to cause prematurity were documented via the study questionnaire and were controlled during the multivariate analysis.
A total of 555 women in the post-partum period were enrolled in the study. Cases and controls were enrolled in a ratio of 1:2 and each enrolled case of premature birth was followed by 2 control cases delivered at term gestation that were next on the register. We used ratio of 1:2 in order to increase the study power and reduce data collection time as there were limited cases of premature birth. In total, there were 185 cases with preterm deliveries/ gestation age of 37 weeks and 370 controls with term delivery/ gestation age >37 weeks.
Data analysis
Descriptive statistics, including chi-square analysis was conducted as part of the background to the main hypothesis testing analysis using multiple logistic regression. The study regression model was built using a hierarchical approach, where the demographic (control) variables were entered first followed by the proposed risk factors. Hierarchical multivariate logistic regression analysis was used with the study variables being entered into the analysis using three groups: the demographic variables that were significant in the univariate analysis (age and employment status) were entered first in the regression model as step 1, followed by the second group in step 2, which included other known potential risk factors also identified as potential confounders in this study such as ever used tobacco, mother’s weight, Inter-conception period, whether premature delivery was experienced before, whether stress was experienced before, malaria during pregnancy, urinary tract infection, physical trauma and violence during pregnancy. The third and final step of the regression analysis, added periodontitis to the model, as it was hypothesized as the study’s main predictor variable.
The odds ratio was calculated with 95% confidence intervals and statistical significance was defined as p < 0.05.