Evaluation of umbilical vein blood flow, fetal oxygen and glucose uptake in uncomplicated monochorionic twins

Introduction: Monochorionic (MC) twins develop under unique intrauterine conditions with a high risk of compromise during fetal life. Non-invasive quantitative assessment of umbilical vein blood flow (UVBF) and estimation of fetal delivery and consumption of oxygen (O2) and glucose have been recently measured for the human fetus under conditions that most nearly represent the undisturbed intrauterine fetal metabolic state. Methods: Here we investigated UVBF, fetal O2 and glucose uptake, as well as umbilical arterial and venous oxygenation and acid-base balance in 24 uncomplicated MC twin pregnancies (48 fetuses) at the time of elective cesarean delivery (36 weeks+4 days +/- 4 days). Twins 1 and 2 were labelled according to birth-order and differences were assessed by Wilcoxon paired test. Results: Significant differences were observed between the two supposedly identical twins of the same mother according to birth order as reported in Table 1. Second-born twins showed significantly lower birthweight and UVBF. Umbilical O2 delivery and uptake per kg were also significantly reduced in the second twin, with a significant relationship between O2 uptake and delivery and between O2 and glucose uptake. Conclusion: The comparison with previous data obtained by our group in singletons suggests the presence of compensatory mechanisms adopted by MC twins to reduce their metabolic needs and adapt to less favourable intrauterine conditions, resembling the findings reported for singleton fetuses with growth restriction. These innovative findings hint at preexisting conditions possibly deriving by uneven metabolic function of the two placental territories and prompt further physiological studies on MC twins and placenta metabolism.