A case control study was conducted at 12 health facilities in the Southern Province of Rwanda from February to August 2018. 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 preterm birth was followed by 2 control cases delivered at term gestation that were next on the register. In total, there were 185 cases with preterm deliveries/ gestation age of 37 weeks or less and low birth weight/ weight of 2500g or less and 370 controls with term delivery/ gestation age >37 weeks and normal birth weight babies/ >2500g.
The study was done in the Southern Province of Rwanda in 6 districts namely; 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. Participants were selected through hospital registers whereby researchers would verify daily to see the cases for preterm deliveries and the controls would be the next 2 on the register. An unmatched case control study design was used but a few key variables like age, smoking habits and presence or absence of systemic conditions were considered for matching. 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 182.
A structured clinical exam and standardized questionnaire was used to collect information regarding the presence of periodontal infection among the pregnant women attending antenatal care clinics in the Southern Province of Rwanda. The study adapted the questionnaire from the WHO Oral Health Assessment Tool for Adults of 201321 to the Rwandan context. The questionnaire was sent to experts for content validation and it was piloted to ensure that it captures all variables as well as ensuring that the questions are clear to the respondents.
The questionnaire was piloted in Nyamata District Hospital in the Eastern Province to ensure for cross-cultural validation and also 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 eg. Smoking, socio-economic status, mother’s weight, number of previous pregnancies, previous preterm or low birth weight and weight gain during pregnancy, illnesses during pregnancy and stress during pregnancy. “Ubudehe” categories in Rwanda are social classes put in place by the Rwanda Ministry of Local Government whereby “people in first category are very poor; do not have a house or cannot afford to pay rent, have a poor diet, cannot get basic household tools and clothes, the second category includes those who have their own houses, can afford to rent a house, mostly get food and earn a wage from with others, the third category includes those who have at least one person in the family working in the government or the private sector and the fourth category includes people who earn high incomes, people who own houses, people who can afford a luxurious lifestyle”22.
A periodontal examination was also done on the women in the study. The trained and calibrated 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 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 additional, a full mouth periodontal screening was done by the researcher and calibrated dental therapists acting as research assistants.
The mothers in the study group were examined at their bedsides by the researcher and calibrated research assistants using a periodontal probe, intra oral 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 gingival margin as a reference point.
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 23. 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 gingival recession was of traumatic origin like in the case of poor brushing techniques, dental caries extending in the cervical area of the tooth and in the cases of recession by malposition of the tooth23.
“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”24. The researcher and research assistants filled in the questionnaires until the required sample was reached.
Multivariate regression analysis was done and the variables were hierarchically grouped into three groups: the demographic variables of age and employment status were put first in the regression model as step 1, followed by the second group (regression model step 2) other potential factors of ever used tobacco, mother’s weight, last pregnancy, whether premature delivery was experienced before, whether stress was experienced before, malaria during pregnancy, urinary tract infection, physical and violence during pregnancy. On the third step of the regression model, the researcher put periodontitis as it was hypothesized as a predictor variable.
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.
The exclusion criteria were postpartum mothers aged 18-35 who delivered singleton babies within 1 to 5 days before recruitment in all selected health facilities. Mothers with twin babies, those with systemic conditions like uncontrolled diabetes, HIV infection and those without teeth in one or more sextants were excluded from the study. Also women whose conditions that could obviously lead to prematurity like abnormal placentation, eclampsia, uterine abnormalities and other pregnancy complications that may easily lead to prematurity were excluded from the study so that they do not bias the results. Other variables that were likely to cause prematurity were taken as covariates and were controlled during multivariate analysis
Descriptive statistics, 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. The odds ratio was calculated with 95% confidence intervals and statistical significance was defined as p < 0.05.