Cardiovascular and Hemodynamic Adaptations in Selective Fetal Growth Restriction: A Cohort Study of Monochorionic Twins.

OBJECTIVE: In monochorionic diamniotic twins with selective fetal growth restriction (sFGR), the Gratacós type is defined by one vessel in one fetus. We asked how much cerebral, venous and myocardial divergence between co-twins it captures. METHOD: Single-center combined retrospective-prospective cohort; one diagnostic examination per pregnancy. Six larger-minus-smaller contrasts were estimated by mixed-effects models on outcome-specific complete pairs. Observed-profile likelihood characterized type-specific phenotypes; HC3 models, bootstrapping and Holm/Benjamini-Hochberg correction tested between-type differences and determinants. RESULTS: Eighty-two pregnancies were included (type I, 27; II, 51; III, 4). The larger co-twin had higher MCA-PI and biventricular MPI and lower MCA-PSV and DV-PIV (all Holm p ≤ 0.006). A coordinated arterial-venous and biventricular profile characterized type II/III alone, yet between-type separation was confined to MCA-PI (1.19 z; 95% CI 0.49-1.88; Holm p = 0.009); neither MPI contrast survived correction. Weight discordance tracked MCA-PSV asymmetry (-0.14 MoM per 10%; Holm p = 0.018), and type modified DV-PIV asymmetry across gestational age (-1.25 z per 2 weeks; Holm p = 0.017), retained excluding type III. CONCLUSION: Umbilical-artery type is mirrored principally by cerebral redistribution. Myocardial alteration is present, including in the larger co-twin, but did not separate types at this sample size, remaining a research phenotype.