Selective Fetal Reduction of Uncomplicated Dichorionic Twins on Parental Request Versus Ongoing Twins and Pregnancy Outcomes: A Systematic Review and Meta-analysis.

Objective: The aim of this study was to assess the effect of elective fetal reduction in uncomplicated twin pregnancies on maternal-fetal outcomes, compared to ongoing twin pregnancies.

Data sources: PubMed, Scopus (until December 2023), and references of retrieved articles.

Study appraisal and synthesis methods: Quality assessment of observational studies was conducted using the ROBINS-I tool. The overall quality of evidence was evaluated per GRADE. A quantitative analysis was performed for electively reduced dichorionic twins. Primary outcome was preterm birth. Secondary outcomes were gestational age at delivery, stillbirth and neonatal intensive care unit, gestational diabetes mellitus, pre-eclampsia, and pregnancy loss < 24 weeks of gestation. Summary odds ratio (ORs) with 95% confidence intervals (CIs) were calculated, and random-effects models were used for data synthesis.

Results: The initial electronic search yielded 745 studies; 175 studies were further identified from reference citations. Five articles included appropriate data and were finally included in the meta-analysis. All studies were evaluated as "moderate risk of bias". Those five studies reported on dichorionic twins. Elective reduction in dichorionic twins reduces the risk for preterm birth <37 weeks (4 studies; n=1577; OR 0.14, 95% CI 0.09-0.22, moderate-quality evidence), <34 weeks (3 studies; n=1335; OR 0.22, 95% CI 0.07-0.69; low-quality evidence), <32 weeks (3 studies; n=1335; OR 0.31, 95% CI, 0.11-0.88; low-quality evidence), gestational diabetes (3 studies; n= 1410; OR 0.57, 95% CI 0.33-0.97, low-quality evidence), pregnancy-associated hypertensive disorders (2 studies; n=581; OR 0.29, 95% CI 0.10-0.83; low-quality evidence), birthweight <10^th centile (2 studies; n=1163; OR 0.27, 95% CI 0.17-0.43; moderate-quality evidence), birthweight< 5^th centile (2 studies; n=1163; OR 0.31, 95% CI 0.19-0.50; low-quality evidence) and increases gestational age at delivery {four studies; n= 1362; MD 2.93 weeks, 95% CI 2.08-3.77; moderate-quality evidence}. The risk for stillbirth (2 studies; n= 1311; OR 1.63, 95% CI 0.43-6.21; very low-quality evidence) or pregnancy loss< 24 weeks (3 studies; n=1436; OR 1.20, 95% CI 0.55-2.58; very low-quality evidence) were not statistically significant different.

Conclusions: Compared to ongoing dichorionic twin pregnancies, dichorionic pregnancies that undergo elective selective fetal reduction are associated with lower incidences of preterm birth < 37 weeks, <34 weeks, <32 weeks, birthweight <10^th centile and <5^th centile, gestational diabetes, hypertensive disorders of pregnancy, and later gestational age at delivery by almost 3 weeks. These associations were often based on very low quality of evidence; so these results should be interpreted with caution and further studies should be conducted.