Assessing the association between periodontitis and preterm low birth weight: A case control study

Premature deliveries are the main causes of prenatal and infant mortality and morbidity in societies and is an important problem in obstetrics. Maternal periodontitis is a very prevalent condition that has suspected to be associated with adverse pregnancy outcomes like preterm birth and low birth weight. However, there are still conicting results and this study have been done to determine the association between periodontitis and preterm low birth weight in order to get necessary information that will enable us to improve mothers’ and children’s health by recommending the screening tool to be used by nurses and midwives to screen for periodontal diseases during antenatal consultations. level, health and lifestyle behavior smoking, social economic category, mothers’ weight, number of previous pregnancies, during during


Abstract
Background Premature deliveries are the main causes of prenatal and infant mortality and morbidity in developed societies and is an important problem in obstetrics. Maternal periodontitis is a very prevalent condition that has suspected to be associated with adverse pregnancy outcomes like preterm birth and low birth weight. However, there are still con icting results and this study have been done to determine the association between periodontitis and preterm low birth weight in order to get necessary information that will enable us to improve mothers' and children's health by recommending the screening tool to be used by nurses and midwives to screen for periodontal diseases during antenatal consultations.

Methods
A case control study was done on 555 women on post-partum period. This case control was in ratio of 1:2; 1 case of preterm and low birth weight to 2 controls. There were 185 cases with preterm deliveries/ gestation age < 37 weeks and low birth weight / weight < 2500 g and 370 controls with term delivery/ gestation age of above or equal to 37 weeks and normal birth weight babies 2500 g and above.
Multivariate regression analysis was done and the variables were hierarchically grouped into three groups: rst categories of demographic variables were put in the regression model as step 1. Second category were other potential factors were put in regression model as the second step. The third category or the third step of regression model, the researcher put periodontitis as it was hypothesized a major predictor variable.

Results
Signi cant association was found between periodontitis and preterm low birth weight; women who had periodontitis had 6 times the odds of giving birth to preterm low birth weight babies compared to women who had no periodontitis (p < 0.001) (95% CI 3.9, 10.4).

Conclusion
Periodontitis is a risk factor for preterm low birth weight and preventive solutions like having a periodontitis screening tool for nurses and midwives during antenatal care consultations are highly recommended.

Background
Premature deliveries are among the leading causes of antenatal and child mortality and morbidity in developed societies. In the United States, prematurity and associated complication such as immature lungs, reduced feeding ability, and poor wait gain caused longer hospital stay, medication with more 70% of prenatal and infant mortality. It has been reported that preterm delivery caused around 28,000 babies died before the age of one year in 2011. Almost a quarter of prematurely born babies were admitted in a hospital at least once during the rst year of life and the increase in hospitalization frequency has been related to the reduced birth weight from 2000 gm 1 .
Neonatal delivery before 37 weeks of gestation is the main cause of low birth weight 2 . Preterm birth is one of the major health care challenges and is associated with many potential consequences like lifelong disabilities and high health care costs 3 . Preterm birth is the leading cause of neonatal death in low income countries 3 . Premature deliveries are around 12.9 million births worldwide representing around 9.6% of all births with some regional discrepancies. African region reported higher incidences of preterm births (18%) followed by USA (12-13%) and Europe (5-9%). According to DHS 2014-2015 in Rwanda, low birth weight deliveries was 6.3% 4 and according to Rwanda Population Reference Bureau, preterm birth complications are part of the top 10 causes of child mortality in Rwanda 5 .
Different studies have identi ed various risk factors that are related to preterm low birth weight and these maternal risk factors include age, weight, socio economic status, smoking, multiple pregnancies, low prenatal care, nutrition, stress, genito-urinary tract infections and Malaria. However, 25% of preterm low birth weight cases was of unknown etiology 6 . There are also various studies that reported on possible association between periodontitis and preterm low birth weight. In 1996, Offenbacher and colleagues were the rst investigators to nd the relationship between maternal periodontitis and premature delivery and later other different authors reported the same ndings 8 , 9 , 10 , 11 . Based on recent published literature, three hypotheses have been identi ed in relation to periodontal bacterial infection and pregnancy outcome. Biological explanations has been hypothesized that including the spread of the germs, the dissemination of the in ammation throughout the body and the activation of the fetomaternal immune system towards the oral pathogens 12 .
In Africa, some studies have associated poor periodontal status with premature birth and low birth weight deliveries. For example, a study done in Nigeria by Umoh and colleagues concluded that the management of periodontal diseases reduced the prevalence of low birth weight deliveries 13 . Although the studies highlighted the association between periodontal infection and the risk of low birth weight, the literature search conducted did not nd any study that pointed out about periodontal screening during pregnancy.
Therefore, the aim of the current study is to assess the association between periodontitis and preterm low birth weight with long term goal of initiating the screening tool to be used by nurses and midwives for screening of periodontitis during antenatal consultations Methods A case control study was done on 555 women on post-partum period. This case control was in ratio of 1:2; 1 case of preterm and low birth weight to 2 control cases. Each selected case of pre-term and low birth weight was followed by 2 control cases that were next on the register but are normal gestation weight. In total, there were 185 cases with preterm deliveries/ gestation age of 37 weeks or less and low birth weight/ weight of 2500 g or less and 370 controls with term delivery/ gestation age > 37 weeks and normal birth weight babies/ >2500 g.
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. It was unmatched case control but some 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 and its association with preterm low birth weight among the pregnant women attending antenatal care clinics in the Southern Province of Rwanda. The study adapted into Rwandan context the questionnaire from WHO Oral health assessment tool for adults of 2013 14 . 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 eastern province to ensure for cross culture 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.
Questionnaire assessed the following variables: Age of the respondent, education level, health and lifestyle behavior like smoking, social economic category, mothers' 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 Rwanda ministry of local government where by "people in rst 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" 15 .
A periodontal examination was also done on the study women. The trained and calibrated examiners used a periodontal to perform the periodontal clinical examination. The examiners were assessing 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 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 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 cemento-enamel junction as a reference point.
The current study de ned periodontitis as presence of pocket depth greater than 3 mm on either maxilla or mandible or both and presence interdental clinical attachment loss (CAL) on ether maxilla, mandible or both of 2 mm or above and buccal or oral CAL of 3 mm or above 16 . 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 + gingival recession; when the gingival margin was on the anatomical crown in case of gingival over growth, CAL was equal to pocket depth -gingival recession. CAL was not considered in some of the speci c cases that were 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 tooth. Researcher and research assistants lled the questionnaires until the 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 rst in the regression model as step 1, followed by the second group (regression model step 2) other potential factors of ever used tobacco, mothers' weight, last pregnancy, whether experienced premature delivery before, whether experiences stress before, malaria during pregnancy, urinary tract infection during pregnancy, physical trauma during pregnancy and violence during pregnancy. On the third step of regression model, the researcher put periodontitis as it was hypothesized as predictor variable.

Results
There were 555 women in their post-partum period that were screened and all questionnaires were lled using structured interview until the sample was accumulated. The participants were from 6 districts of Southern province of Rwanda and from 12 health facilities. The participants were distributed with respect to age, education level, employment status, social economic status. The mean age was 27.35 (SD = 5.2) ranging from 18 to 35 years. Most participants (n = 338, 60.9%) were in the age range of 26-35 years, 47.6% had primary education, 38.7%, had secondary education, 7% had tertiary education and 6.7% had no formal education. The majority of the study participants, (n = 513, 92.4%) are from rural setting, 63.2% are farmers and 55.5% are in category 3 of "Ubudehe"/ social economic status as categorized in Rwanda national categories. Factors associated with preterm low birth weight among pregnant women attending antenatal care clinics To assess if there is a relationship between women who had periodontal diseases and those who had health gingiva in relation to preterm low birth weight, in our sample we had 370 women with normal gestation and normal birth weight babies (controls). On another group we had 185 (cases) women who had given birth prematurely and with low birth weight babies. Among the women with normal gestational age and normal weight babies, 229 (61.8%) had healthy periodontium while 141(38%) had periodontitis.
On the other hand, among women with preterm low birth weight, 31 (16.7%) had healthy periodontium and 154 (83.2%) had periodontitis, chi-square test revealed that periodontal disease is signi cantly associated with preterm and low birth weight (x 2 = 100.902, p < 0.001). There was also a signi cant association between preterm low birth weight and mothers' weight where by mothers with less weight were found to be with high chances of having periodontitis compared to those with normal weight (x 2 = 29.198, p < 0.001), Last pregnancy was also found to be signi cantly associated with preterm low birth weight where by the mothers who got pregnant before 24 months after delivery were found to be with high risk of preterm low birth weight compared to those who got pregnancy 24 months and above after previous delivery (x 2 = 19.474, p < 0.001), Women who had experienced premature deliveries before had higher chances of preterm low birth weight (x 2 = 47.989, < 0.001), stress during pregnancy was also found to be associated with preterm low birth weight, where by the mothers who reported stress during pregnancy had high risk of preterm low birth weight compared to those who reported no stress (x 2 = 15.711, p < 0.001), some illnesses during pregnancy were also associated with preterm low birth weight like Malaria (x 2 = 5.686, p = 0.021), Urinary tract infection (x 2 = 5.382, p = 0.020). On the other hand, violence during pregnancy was also found to be signi cantly associated with preterm low birth weight (x 2 = 20.321, p = < 0.001). Age, education level and residence are not associated with preterm low birth weight (x 2 0.639, p = 0,2), (x 2 5.862, p = 0.1), (x 2 1.855, p = 0.2) respectively. Chi-square test revealed association between tobacco and preterm low birth weight. Women who had ever used tobacco had high chances of having preterm low birth weight compared to those who had never used tobacco (x 2 = 4.630, p < 0.04).  During bivariate analysis using chi square test, 11 variables namely; employment status, ever used tobacco, periodontitis, mothers' weight, last pregnancy, malaria during pregnancy, urinary tract infection during pregnancy, experienced premature delivery before, experienced stress during pregnancy and violence during pregnancy were associated with Preterm low birth weight therefore, eligible for multivariate logistic regression. Multivariate regression analysis was done and the variables were hierarchically grouped into three groups: where by demographic variable of employment status was put rst in the regression model as step 1 and followed by other potential factors of ever used tobacco, mothers' weight, last pregnancy, whether experienced premature delivery before, where experiences stress before, Malaria during pregnancy, urinary tract infection during pregnancy, physical trauma during pregnancy and violence during pregnancy. On the third step of regression model, the researcher put periodontal diseases as it was hypothesized as predictor variable.
Employment status and ever used tobacco lost their signi cance after controlling for other variables (p = 0.4, 95% CI 0.3, 1.2), (P = 0.2, 95% CI 0.5,15.8) respectively but some other variables remained signi cant. After building the regression model, the results were as follows; the logistic regression revealed that mothers' weight was still signi cant after controlling for other variables, mothers with less weight had higher chances of giving birth to preterm and low birth weight babies compared to mother with normal weight where by the odds of giving birth to preterm low birth weight baby was 6 times for underweight compared to those with normal weight mothers (p = 0.002) (95% CI 1 1.5, 27.9). Also the results from logistic regression revealed that women with history of giving birth to premature babies before, had higher chances of preterm low birth weight babies where by the odds of preterm low birth weight when you had ever experienced premature delivery was 14 times higher compared to those who had no history of premature deliveries (p < 0.001) (95% CI 3.4, 45.9). It was also found out that women who had experienced violence during pregnancy had 6 times the odds of having preterm low birth weight compared to those who did not experience any violence during pregnancy (p = 0.007) (95% CI 1.6, 20.0). Also interval between pregnancies was found to be associated with preterm low birth weight where by women who got pregnancy before 24 months after last delivery had 2 times odds of having preterm low birth weight compared to women who got pregnant 24 months above after previous delivery (p < 0.008) (95% CI 1.2, 3.6). Finally, logistic regression revealed strong association between periodontitis and preterm low birth weight where by women who had periodontitis had 6 times the odds of giving birth to preterm low birth weight babies compared to women who had no periodontitis (p < 0.001) (95% CI 3.9, 10.4). Table 3  Table 3 Multivariate analysis of Preterm low birth weight and associated factors  20 , 21 . Though majority of the studies found out that the older maternal age was associated with higher risk of preterm low birth weight. Ambrogio and colleagues in their study observed that both extreme ages that is, maternal age under 17 and advanced age over 40 were independent factor for preterm low birth weight (OR 2.97; 95% CI 1.24, 7.14, P < 0.005) 18 . This was echoed by Florent and coauthors who also found that both advanced age and lower age were risk factors for preterm low birth weight 20 . On the hand Mumghamba in Tanzania compared mothers who had PTLBW babies with and normal weight babies and found out that PLBW had a lower mean age 22 . Our study shows no association between maternal age and preterm low birth weight. In this study, most of the mothers were young whereby the mean age was 27.35 (SD 5.2) ranging from 18 to 35 years and may be the reason why there was no statistical association between maternal age and preterm low birth weight in this study.
Similarly the study done in Uganda by Muwazi who also worked on a young population which led to low prevalence of periodontitis and later led to reduced statistical power and therefore no association was found 23 .
Maternal weight was also reported to be associated with preterm low birth weight where by in our study the logistic regression revealed that mothers with less weight had higher chances of pre-mature deliveries and low birth weight babies as opposed to mother with normal weight where by the odds of having preterm low birth weight baby was 6 times for underweight compared to those with normal weight mothers (p = 0.002) (95% CI 1.5, 27.9). Our study ndings were echoed by Zhen and colleagues who revealed that neonates born to underweight mothers had higher r of preterm and low birth weight (95% CI 1.14, 1.25, RR 1.21) 24 . Many other variables were found to be associated with preterm low birth weight in this study were; interval between last pregnancy and the current, previous preterm birth, stress during pregnancy and illnesses during pregnancy. However, 25% of the cases was a proportion of preterm low birth weight of unknown etiology 6 .
In this study, the presence or absence of periodontitis disease was major predictor of pre-term delivery and low birth weight. After controlling for other variables logistic regression revealed strong association between periodontitis and preterm low birth weight where periodontitis could lead to six fold higher the risk of giving birth to preterm low birth weight babies compared to women who had no periodontitis (p < 0.001) (95% CI 3.9, 10.4). Nevertheless, our study results are controversial to some other studies like the study done in Germany by Noack and colleagues who did not nd any association between periodontitis and preterm low birth weight 25 . Similarly, Davenport in 2002 in his case control study did not detect any association between periodontitis and preterm low birth weight 26 and also Mumghamba in Tanzania in 2017 did not nd any evidence to support periodontitis to be associated with preterm low birth weight 22 .
However, our study is echoed by several other studies that supported the association between periodontitis and preterm low birth weight.  reported for the rst time that there is a possible relationship between maternal periodontitis and delivery of a preterm infant where they reported that periodontitis during pregnancy could lead to seven times more risk of preterm birth 6 . In a systematic review by Teshome in 2016, he revealed the association between periodontitis and preterm low birth weight 27 . Lopez and colleagues also assessed the risk of preterm birth and low birth weight in women with periodontitis in the USA and found that pregnant women with periodontitis were at a higher risk of giving birth to premature babies with low birth weight (p = 0.0004; RR = 3.5) 28 . Several other studies also con rmed the association 9 , 29 , 10 , 30 , 31 , 32 . Also in Africa, some studies have been done on preterm birth and Low birth weight deliveries and these were signi cantly associated with poor periodontal status; for example a study done in Nigeria by Umoh and colleagues reaveled that periodontal treatment was effective in preventing low birth weight deliveries 13 . In Uganda, Wandera and colleagues also found out that mothers having periodontal problems and poor oral hygiene during pregnancy had a greater risk of preterm low birth weight and opposed to mothers who had not periodontis during pregnancy 33 and Muwazi in Uganda in his cross sectional study revealed the association between gingival recession and preterm birth 23 .

Conclusion:
Periodontitis is a risk factor for preterm low birth weight and prevention solutions like having a periodontitis screening tool for nurses and midwives during antenatal care consultations are highly recommended. Ethics approval and consent to participate: Permission to conduct the study was sought from the ethics committee of the University of Rwanda, College Medicine and Health Sciences and approval from study sites. Also permission from the Ministry of health to conduct study in the selected health facilities was sought and granted. Informed consent forms were given to the participants. Participants were informed that they have right to withdraw at any time and that their participation was be entirely voluntary. The participants were given the information sheet containing all the information about the study and those who did not know how to read, we read for them. After understanding the study bene ts and risks and everything that was involved in the study, those who agreed were given the consent form to sign that they have voluntarily agreed to participate in the study. Information from the participants was be kept con dential and used for study purposes.
Consent for publication: