Oral microflora and pregnancy: a systematic review and meta-analysis

Abstract

Understanding changes in oral flora during pregnancy, its association to maternal health, and its implications to birth outcomes is essential. We searched PubMed, Embase, Web of Science, and Cochrane Library in May 2020 (updated search in April and June 2021), and conducted a systematic review and meta-analyses to assess the followings: (1) oral microflora changes throughout pregnancy, (2) association between oral microorganisms during pregnancy and maternal oral/systemic conditions, and (3) implications of oral microorganisms during pregnancy on birth outcomes. From 3983 records, 78 studies were included for qualitative assessment, and 13 studies were included in meta-analysis. The oral microflora remains relatively stable during pregnancy; however, pregnancy was associated with distinct composition/abundance of oral microorganisms when compared to postpartum/non-pregnant status. Oral microflora during pregnancy appears to be influenced by oral and systemic conditions (e.g. gestational diabetes mellitus, pre-eclampsia, etc.). Prenatal dental care reduced the carriage of oral pathogens (e.g. Streptococcus mutans). The Porphyromonas gingivalis in subgingival plaque was more abundant in women with preterm birth. Given the results from meta-analyses were inconclusive since limited studies reported outcomes on the same measuring scale, more future studies are needed to elucidate the association between pregnancy oral microbiota and maternal oral/systemic health and birth outcomes.

Figure 1

Flow diagram of study identification. The 4-phase preferred reporting items for systematic reviews and meta-analyses (PRISMA) flow diagram was used to determine the number of studies identified, screened, eligible, and included in the systematic review and meta-analysis (http://www.prisma-statement.org).

Figure 2

Summary of quality and risk of bias assessment using the Cochrane Collaboration’s tool for assessing risk of bias in randomized trials and the adapted Downs and Black scoring tool.

Figure 3

Impact of pregnancy status on subgingival plaque total bacterial carriage. (A) Mean difference of total bacterial carriage in subgingival plaque between different trimesters of pregnancy. (B) Mean difference of total bacterial carriage in subgingival plaque between pregnancy and postpartum. (C) Mean difference of total bacterial carriage in subgingival plaque between pregnant women and non-pregnant women. Study heterogeneity (I²) and the related p value were calculated using the continuous random effect methods. The Mean Difference, 95% CI of each study included in the meta-analyses and forest plots of comparisons shown in A-1 through C-3 indicate that, regarding total bacterial carriage in subgingival plaque, there is no statistically difference between each stage of pregnancy (p > 0.05), between postpartum and pregnancy (p > 0.05), and between non-pregnant and pregnant women (p > 0.05).

Figure 4

Impact of pregnancy status on salivary total bacterial carriage. Mean Difference of salivary total bacterial carriage in non-pregnant and 2nd trimester pregnant women. Study heterogeneity (I²) and the related p value were calculated using the continuous random effect methods. The Mean Difference, 95% CI of each study included in the meta-analysis and forest plot of comparisons indicate that, regarding salivary total bacterial carriage, there is no statistically significant difference between non-pregnant and 2nd trimester pregnant women (p > 0.05).

Figure 5

Impact of pregnancy status on the carriage of periodontal pathogens in subgingival plaques. (A) Carriage of A. actinomycetemcomitans during pregnancy trimesters (A-1) and between pregnancy and postpartum (A-2). (B) Carriage of P. gingivalis during pregnancy trimesters (B-1) and between pregnancy and postpartum (B-2). (C) Carriage of T. forsythia between postpartum and 2nd trimester. (D) Carriage of T. denticola between postpartum and 2nd trimester. Study heterogeneity (I²) and the related p value were calculated using the continuous random effect methods. The Mean Difference, 95% CI of each study included in the meta-analyses and forest plots of comparisons shown in (A–D) indicate that, regarding the carriage [measured by colony forming unit (CFU)] of four different periodontal pathogens in subgingival plaque, there is no statistically significant difference between stages of pregnancy and between postpartum and pregnancy (p > 0.05).

Figure 6

Impact of pregnancy status on salivary Candida carriage. The Mean differences of Candida carriage between 1st and 3rd trimester (A), between non-pregnancy and 1st trimester (B), and between non-pregnancy and 3rd trimester (C) indicated that oral Candida remain stable during the pregnancy and no differences (p > 0.05) are detected between pregnant and non-pregnant women. Study heterogeneity (I²) and the related p value were calculated using the continuous random effect methods.

Figure 7

Effect of prenatal dental treatment on salivary S. mutans reduction. A meta-analysis was performed on two studies that assessed salivary S. mutans carriage before and after receiving prenatal dental treatment. Study heterogeneity (I²) and the related p value were calculated using the continuous random effect methods. The Mean Difference, 95% CI of each study included in the meta-analysis and forest plot of comparison indicate that, regarding salivary S. mutans carriage, there is no statistically significant difference before and after prenatal dental treatment (p = 0.38).