Effects of tea consumption during pregnancy on preterm birth and small for gestational age: A systematic review

Abstract

Purpose Tea consumption during pregnancy is assumed to increase the risks of preterm birth and small for gestational age (SGA). However, this association remains unclear. This review aimed to assess the effects of tea consumption during pregnancy on preterm birth and SGA. Method A search through 4 databases (PubMed, CINAHL, CiNii, and Ichushi-Web) and handsearches were conducted for identifying relevant publications in Japanese and English. We first screened the identified articles based on the inclusion and exclusion criteria and then evaluated the quality of articles using a risk-of-bias assessment tool. We used Mantel-Haenszel test to integrate the results of articles included in the review. Results Eleven articles were included in the review. Five articles examined the association between any tea consumption during pregnancy and preterm birth. Among the 5 articles, a meta-analysis of 3 articles that had the similar classification criteria for tea consumption indicated that the risk of preterm birth was significantly higher in women with high tea consumption (3 or more cups per week or 1 or more cups per day) than in women with low tea consumption (odds ratio=1.32, 95% confidence interval=1.06-1.63). By tea type, the consumption of green, Japanese and Chinese, or black tea was associated with an increased risk of preterm birth in 3 out of 7 relevant articles. However, meta-analyses showed no significant associations between the consumption of green or black tea and preterm birth. Black tea consumption during pregnancy was reported to be associated with an increased risk of SGA in 1 out of 7 relevant articles. In meta-analysis, no significant association between black tea consumption and SGA was found. Conclusion The meta-analysis showed an association between any tea consumption and preterm birth. On the other hand, there was no association between tea consumption and SGA. Further research regarding an association between tea consumption and SGA is required because of the small number of studies that could be used in the meta-analysis. Healthcare professionals would need to grasp individual daily tea consumption and inform pregnant women of the possible association between high tea consumption and an increased risk of preterm birth.