Table 1.

Summary of characteristics of studies included in the systematic review

Characteristic	Total	M. hominis	U. urealyticum	U. parvum
Number of studies, n*	53	42	19	14
Study design, n
Cohort	26	22	10	7
Case-control	22	16	8	6
Cross-sectional	5	4	1	1
Number of women, total (median; IQR)	37 132 (241; 145–688)	29 989 (250; 164–765)	10 732 (214; 114–783)	9890 (215; 145–972)
Study setting, income category, n
High income	36	27	14	12
Upper-middle income	9	8	3	2
Lower middle-income or low	2	2	0	0
Not reported	6	5	2	0
Outcomes reported, n*
Preterm birth	40	30	16	13
Low birth weight	7	6	2	1
Premature rupture of membranes	13	11	3	2
Spontaneous abortion	10	10	4	2
Perinatal death	9	9	1	1
Specimen type, n†
Endocervical swab	24	20	7	6
Vaginal swab	13	6	6	5
Urine	1	1	0	0
Amnotic fluid	8	5	4	1
Placental membrane	7	6	2	2
Diagnostic method*
NAAT	22	13	16	11
Culture	28	28	0	0
Culture and NAAT	3	1	3	3
Other‡	1	1	0	0
Bacterial vaginosis assessed, n	11	10	1	1
Reported presence of STI, n	21	22	7	7
Reported on smoking status, n	14	6	3	3
Reported on multiple pregnancy, n
Excluded	26	20	11	8
Included	9	6	4	3

*The total number of studies included is 53. The totals for each organism and outcome sum to more than 53 because one study might have reported on more than one organism and outcome.

†One study used both urine and endocervical swab.

‡ELISA (with NAAT/Culture).

ELISA, Enzyme-linked immunosorbent assay; NAAT, nucleic acid amplification test; STI, sexually transmitted infection.