Table 3. Alterations of the gut microbiota in the GDM women compared to the non-GDM women.

Studies	Liu et al. 2020 [40]	Mokkala et al. 2020 [45]	Zheng et al. 2020 [49]	Ma et al. 2020 [46]	Mokkala et al. 2017 [47]	Gomez-Arango et al. 2016 [48]	Koren et al. 2012 [12]	Wang et al. 2020 [50]	Liu et al. 2020 [40]	Chen et al. 2020 [51]	Zheng et al. 2020 [49]	Kuang et al. 2017 [52]	Li et al. 2021 [54]	Xu et al. 2020 [53]	Cui et al. 2020 [55]	Wu et al. 2019 [56]	Liu et al. 2019 [57]	Cortez et al. 2018 [58]	Wang et al. 2018 [59]	Crusell et al. 2018 [60]	Koren et al. 2012 [12]	Crusell et al. 2018 [60]	Fugmann et al. 2015 [61]	Hasan et al. 2018 [62]	Hou et al. 2020 [63]
Time-point	First trimester/ early pregnancy							Second trimester						Third trimester								Postpartum			?	Total
Beta diversity																										Total D	Total N
Beta diversity	N	N	N	D		N	N	D	D	D	N	D	D	D	N	D		N	D	N	N	N	N	N		9	13
Alpha diversity																										Total ↓	Total ↑
Richness	↓	N		↓				N	↓	↓		↓	N	N			↓	↑		N		N	N	N		6	1
Evenness		N	N	↓↑			N	↓	↓	↓	N	↓	↑	N		N	↓	N		N		N	N	N		6	2
Phylum level																										Total ↓	Total ↑
Actinobacteria										↓										↑		↑			↑	1	3
Bacteroidetes									↓	↑			↓												↑	2	2
Firmicutes										↓			↑										↓		↓	3	1
Class level																										Total ↓	Total ↑
Actinobacteria										↓										↑		↑				1	2
Bacteroidia					↓					↑			↓													2	1
Clostridia					↑					↓			↑													1	2
Order level																										Total ↓	Total ↑
Coriobacteriales													↑							↑		↑				0	3
Clostridiales					↑							↓	↑													1	2
Family level																										Total ↓	Total ↑
Coriobacteriaceae												↓	↑							↑		↑				1	3
Lachnospiraceae								↓↑					↑					↑								1	3
Ruminococcaceae					↑			↓					↑					↑								1	3
Genus level																										Total ↓	Total ↑
Collinsella													↑					↑		↑		↑				0	4
Eggerthella											↑	↓										↓				2	1
Bacteroides										↑								↑		↓		↓				2	2
Ruminococcus2								↓												↑		↓				2	1
Blautia									↑				↑					↑		↑						0	4
Coprococcus			↓								↓		↑													2	1
Roseburia								↑				↓						↑								1	2
Faecalibacterium								↓	↑								↓			↓↑		↓↑				4	4
Fusobacterium												↓							↑			↓				2	1
Sutterella										↑			↓							↓						2	1
Akkermansia								↑	↓								↑									1	2

Bacteria are illustrated if they are significantly different in relative abundance between cases and controls in 3 or more of the included studies. ↑ indicates a higher alpha diversity or bacteria are more abundant in the GDM group compared to the control group. ↓ indicates a lower alpha diversity or bacteria are less abundant in the GDM group compared to the control group. ↓↑ indicates significantly differences in opposing directions in alpha diversity or specific bacteria abundance. D indicates a significant difference in beta diversity between the GDM and the control group. N indicates no difference in beta diversity between the groups. A question mark (?) indicates unknown sample collection time point.