ORIGINAL ARTICLE Longitudinal reference ranges for serial measurements of myocardial performance index (MPI) by conventional and pulsed‐wave tissue Doppler in monochorionic diamniotic twins at 17 to 26 weeks of gestation Cristina Zanardini 1,2 | Anna Fichera 1 | Stefano Calza 3 | Veronica Cappa 3,4 | Rossana Orabona 1 | Tiziana Frusca 1,5 | Federico Prefumo 1 1 Department of Obstetrics and Gynaecology, University of Brescia, Brescia, Italy 2 PhD Programme in Reproduction and Development, University of Trieste, Trieste, Italy 3 Section of Medical Statistics and Biometry, Department of Biomedical Sciences and Biotechnology, University of Brescia, Brescia, Italy 4 Big&Open Data Innovation Laboratory (BODaI‐Lab), University of Brescia, Brescia, Italy 5 Department of Surgical Sciences, Obstetrics and Gynaecology Unit, University of Parma, Parma, Italy Correspondence Federico Prefumo, Dipartimento di Ostetricia e Ginecologia, Università di Brescia, Piazzale Spedali Civili, 1, 25123 Brescia, Italy. Email: federico.prefumo@gmail.com Abstract Objective: To describe the longitudinal changes of fetal myocardial performance index (MPI) measured by conventional Doppler (MPI) and by pulsed‐wave tissue Doppler (MPI′) based on a prospective cohort of uncomplicated monochorionic diamniotic twin. Method: Single‐center observational study. We measured MPI and MPI′ in the right and left ventricles 3 times between 17 and 26 weeks of gestation. Second‐degree fractional polynomials were built to obtain the best fitting curves in relation to gesta- tional age (weeks) for each parameter. Gestational age‐specific reference values were estimated by using two‐level hierarchical models. Results: Eighty‐three uncomplicated monochorionic pregnancies were included in our study with a total of 249 observations. Fetal cardiac function was measured as MPI RV and LV, MPI′ RV and LV at a mean gestational age of 18 +3 (range 17 +1 to 19 +2 ), 22 +3 (21 +1 to 23 +5 ), and 24 +3 (22 +6 to 26 +2 ) weeks. The reference ranges for MPI LV, MPI RV, MPI′ LV, and MPI′ RV at 17 to 26 weeks were constructed and con- ditional percentiles calculated. Conclusion: The present study provides additional data on fetal cardiac function in uncomplicated monochorionic diamniotic twin gestations, describing the evolution of MPI and MPI′ in both ventricles in uncomplicated monochorionic diamniotic pregnancies. 1 | INTRODUCTION Evaluation of cardiac function is being increasingly used in fetal med- icine as a research and clinical tool in a wide range of fetal diseases, such as twin‐to‐twin transfusion syndrome (TTTS) and fetal growth restriction. 1-8 Assessment of fetal cardiac function is mainly performed by conventional echocardiographic techniques such as M‐mode, B‐ mode, and pulsed Doppler and, more recently, by tissue Doppler imag- ing (TDI), which is a reproducible echocardiographic tool that permits a quantitative assessment of motion and timing of myocardial events. 4,9,10 The myocardial performance index (or Tei index or MPI) is a Doppler‐based method to assess the cardiac function which has been introduced and validated in fetal medicine. 5 It compares the time the heart spends in isovolumic relaxation and in isovolumic contrac- tion with the ejection time from simultaneous Doppler assessment of mitral‐aortic or tricuspid‐pulmonary flow or tissue profiles and can be measured by conventional pulsed Doppler (MPI) and by TDI (MPI′). Monochorionic twin pregnancy is complicated in at least 10% of cases by TTTS, a condition characterized by hemodynamic modifica- tions and varying degrees of cardiac dysfunction. Prediction of Received: 2 March 2018 Revised: 16 May 2018 Accepted: 17 May 2018 DOI: 10.1002/pd.5286 Prenatal Diagnosis. 2018;38:591–600. © 2018 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/pd 591