Table 1. Characteristics of the included studies in the meta-analysis.
| Author [publication year] | Nation | Sample size | Study design | Mean age (SD) in metformin group | Mean age (SD) in control group | Mean BMI (SD) in metformin group |
Mean BMI (SD) in control group | Follow-up duration | Main outcomes |
|---|---|---|---|---|---|---|---|---|---|
| Vanky E [2004] | Norway | 40 | RCT | 28.6±4.2 | – | 30.6±7.3 | – | During pregnancy | Severe pregnancy or post partum complications, preterm delivery |
| Vanky E [2010] | Norway | 274 | RCT | 29.6±4.4 | 29.2±4.4 | 29.5±7.0 | 28.5±7.2 | During pregnancy | Preeclampsia, preterm delivery, gestational diabetes mellitus |
| Underdal MO [2018] | Norway | 274 | Follow-up study of an RCT | 37.5±4.2 | – | 29.6±6.9 | – | 7.7 years after pregnancy | Type 2 diabetes mellitus, depression |
| Salvesen KA [2007] | Norway | 40 | RCT | 28.9 (4.8) | 28.3 (3.7) | 32.1 (6.1) | 29.3 (8.0) | From 6–12 (mean: 8) gestational weeks to birth | Pregnancy complications, cesarean section, persistent nausea and gastrointestinal discomfort, preterm delivery, preeclampsia, postpartum streptococcus sepsis |
| Løvvik TS [2019] | Norway, Sweden, and Iceland | 468 | RCT | 29 (24–34) | 30 (24–36) | 27.5 (18.2–36.5) | 26.7 (18.8–34.6) | During pregnancy | Miscarriage, GDM, preterm delivery, PIH |
| Hjorth-Hansen A [2018] | Norway | 258 | RCT | 29.6 (4.3) | 29.3 (4.4) | 29.6 (7.3) | 28.2 (6.4) | During pregnancy | Birth weight, birth length |
| Greger HK [2020] | Norway | 93 | Follow-up of 2 randomized, placebo-controlled trials | 29.3 (3.4) | 29.0 (4.3) | 30.2 (7.0) | 27.9 (6.3) | 7.7 years | GDM, preeclampsia, preterm delivery |
| Fougne KJ [2008] | Norway | 40 | RCT | 28.9 (26.5–31.4) | 28.3 (26.6–30.0) | 29.3 (25.8–32.9) | 32.1 (29.1–35.2) | During pregnancy | GDM |
| Carlsen SM [2012] | Norway | 199 | Follow-up study of RCT | 29.7 (4.4) | 29.4 (4.3) | 29.5 (7.1) | 27.6 (6.1) | 1 year after birth | 1-year postpartum BMI |
| Carlsen SM [2010] | Norway | 40 | Follow-up study of RCT | – | – | – | – | During pregnancy | SHBG levels, dihydrotestosterone |
| Begum MR [2009] | Bangladesh | 59 | RCT | 28.14 (2.92) | 26.13 (3.62) | 28.21 (2.37) | 27.97 (2.49) | During pregnancy | GDM, miscarriage, preterm labor |
| Abdalmagee OS [2019] | Egypt | 102 | RCT | 31.1±3.7 | 31.89±3.6 | 33.8±4.4 | 32.9±6.7 | During pregnancy | Miscarriage |
| Wang Aiping [2018] | China | 72 | RCT | 30.8±3.0 | 30.0±2.7 | – | – | During pregnancy | Fasting glucose, insulin, HbA1c (%) |
| Rø TB [2012] | Norway | 25 | Follow-up study of an RCT | 8.2 (0.6) | 8.1 (0.8) | 1.09 (0.91) | 1.05 (1.06) | 8 years after birth | Birth weight, BMI (SDS) at 8 years old |
| Morin-Papunen L [2012] | Finland | 135 | RCT | 28.4 (3.9) | 27.9 (4.1) | 27.1 (6.3) | 26.9 (6.2) | During pregnancy | Live birth |
| Hanem LGE [2019] | Norway | 139 | Follow-up of randomized, placebo-controlled trials | 29.5±3.9 | 30.2±4.2 | 29.0±6.9 | 28.4±6.3 | 4 years after birth | BMI at 4 years, waist circumference, body fat |
| Hanem LGE [2018] | Norway | 141 | Follow-up of randomized, placebo-controlled trials | – | – | 17.8 (17.0 to 18.5) | 16.8 (16.2 to 17.3) | 5–10 years after birth | Birth length, birth weight |
| Hanem LGE [2021] | Norway | 62 | Follow-up of randomized, placebo-controlled trials | 7.40 ± 1.21 | 7.46 ± 1.18 | – | – | 5–10 years after birth | Androstenedione, 11-deoxycortisol |
BMI, body mass index; GDM, gestational diabetes mellitus, RCT, randomized controlled trial; BMI SDS, standardized BMI.