AIM To investigate the effect of disease activity or thiopurine use on low birth weight and small for gestational age in women with inflammatory bowel disease(IBD).METHODS Selection criteria included all relevant articles on the effect of disease activity or thiopurine use on the risk of low birth weight(LBW) or small for gestational age(SGA) among pregnant women with IBD. Sixtynine abstracts were identified,35 papers were full text reviewed and,only 14 of them met inclusion criteria. Raw data were extracted to generate the relative risk of LBW or SGA. Quality was assessed using the Newcastle Ottawa Scale.RESULTS This meta-analysis is reported according to PRISMA guidelines. Fourteen studies met inclusion criteria,and nine reported raw data suitable for meta-analysis. We found an increased risk ratio of both SGA and LBW in women with active IBD,when compared with women in remission: 1.3 for SGA(4 studies,95%CI: 1.0-1.6,P = 0.04) and 2.0 for LBW(4 studies,95%CI: 1.5-2.7,P < 0.0001). Women on thiopurines during pregnancy had a higher risk of LBW(RR 1.4,95%CI: 1.1-1.9,P = 0.007) compared with non-treated women,but when adjusted for disease activity there was no significant effect on LBW(RR 1.2,95%CI: 0.6-2.2,P = 0.6). No differences were observed regarding SGA(2 studies; RR 0.9,95%CI: 0.7-1.2,P = 0.5). CONCLUSION Women with active IBD during pregnancy have a higher risk of LBW and SGA in their neonates. This should be considered in treatment decisions during pregnancy. AIM To investigate the effect of disease activity or thiopurine use on low birth weight and small for gestational age in women with inflammatory bowel disease (IBD). METHODS Selection criteria included all relevant articles on the effect of disease activity or thiopurine use on the risk of Low birth weight (LBW) or small for gestational age (SGA) among pregnant women with IBD. Sixtynine abstracts were identified, 35 papers were full text reviewed and, only 14 of them met inclusion criteria. Raw data were extracted to generate the relative risk of LBW or SGA. Quality was assessed using the Newcastle Ottawa Scale .RESULTS This meta-analysis is reported according to PRISMA guidelines. Fourteen studies met inclusion criteria, and nine reported raw data suitable for meta-analysis. We found an increased risk ratio of both SGA and LBW in women with active IBD, when compared with women in remission: 1.3 for SGA (4 studies, 95% CI: 1.0-1.6, P = 0.04) and 2.0 for LBW 2.7, P <0.0001). Wom en on thiopurines than pregnancy had a higher risk of LBW (RR 1.4, 95% CI: 1.1-1.9, P = 0.007) compared with non-treated women, but when adjusted for disease activity there was no significant effect on LBW , 95% CI: 0.6-2.2, P = 0.6). CONCLUSION Women with active IBD during pregnancy have a higher (2 studies; RR 0.9, 95% CI: 0.7-1.2, P = risk of LBW and SGA in their neonates. This should be considered in treatment decisions during pregnancy.