Weight discordance and perinatal mortality in twin pregnancies: a systematic review and meta-analysis

OBJECTIVES: The primary aim of this systematic review was to explore the strength of association between birthweight (BW) discordance and perinatal mortality in twin pregnancies; the secondary aim was to ascertain the contribution of gestational age and growth restriction in determining mortality in growth discordant twins. METHODS: Medline, Embase, Cinahl and Clinicaltrials.gov databases were searched. Only studies reporting the risk of mortality in twin pregnancies affected compared to those not affected by weight discordance were included. The weight discordance cut-offs considered were ≥15%, ≥20%, ≥25%, ≥30%. Meta-analyses using individual data random-effect logistic regression and meta-analyses of proportion were used to analyse the data. RESULTS: Twenty-two studies (10877 twin pregnancies) were included. In DC pregnancies, the overall risk of IUD, but not of NND, was higher in twins with ≥15% (OR: 9.8, 3.9-29.4), ≥20% (OR: 7.0, 95% CI 4.15-11.8), ≥25% (OR: 17.4, 95% CI 8.3-36.7) and ≥30% (OR: 22.9, 95% CI 10.2-51.6) BW discordance compared to controls. For each cut-off of BW discordance explored, the smaller twin was at higher risk of mortality compared to the larger one. In MC twin pregnancies, twins discordant ≥20% (OR: 2.8, 95% CI 1.3-5.8) or ≥25% (OR: 3.2, 95% CI 1.49-6.67) were at higher risk of IUD, compared to controls once cases affected by twin-to twin transfusion syndrome were excluded. Twin pregnancies with ≥25% weight discordance were also at risk of NND (OR: 6.77, 95% CI 2.25-20.4). The risk of IUD was higher when considering only discordant pregnancies containing at least an SGA fetus. The overall risk of mortality was not different between the smaller and larger twin except for a weight discordance of ≥20% CONCLUSION: DC and MC twin pregnancies discordant for fetal growth are at higher risk of IUD but not NND compared to concordant twins. The risk of IUD in discordant DC and MC twins is higher when at least one fetus is SGA