Objective To evaluate the performance of fetal middle cerebral artery peak systolic velocity (MCA‐PSV) ≥ 1.5 multiples of the median (MoM) for the prediction of moderate–severe anemia, in untransfused and transfused fetuses. Methods A systematic search was performed to identify relevant observational studies reported in the period 2008–2018 that evaluated the performance of MCA‐PSV, using a threshold of 1.5 MoM for the prediction of fetal anemia. Diagnosis of fetal anemia by blood sampling was the reference standard. A hierarchical summary receiver–operating characteristics (hSROC) curve was constructed using random‐effects modeling. Subgroup and meta‐regression analyses, according to the number of previous intrauterine transfusions, were performed. Results Twelve studies and 696 fetuses were included in the meta‐analysis. The area under the hSROC curve (AUC) for moderate–severe anemia was 83%. Pooled sensitivity and specificity (95% CI) were 79% (70–86%) and 73% (62–82%), respectively, and positive and negative likelihood ratios were 2.94 (95% CI, 2.13–4.00) and 0.272 (95% CI, 0.188–0.371). When considering only untransfused fetuses, prediction improved, achieving an AUC of 87%, sensitivity of 86% (95% CI, 75–93%) and specificity of 71% (95% CI, 49–87%). A decline in sensitivity for the prediction of moderate–severe anemia by MCA‐PSV ≥1.5 MoM was observed (estimate, –5.5% (95% CI, –10.7 to –0.3%), P = 0.039) as the number of previous transfusions increased. Conclusions MCA‐PSV ≥ 1.5 MoM for the prediction of moderate–severe anemia in untransfused fetuses shows moderate accuracy (86% sensitivity and 71% specificity), which declines with increasing number of intrauterine transfusions. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Key Clinical MessageTrisomy 9 can be suspected and confirmed in the prenatal period since the 11–13.6 weeks of screening. In cases of partial trisomy 9, the diagnosis is important especially to counseling the couple due to the increased likelihood of recurrence in subsequent pregnancies.

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