Healthy Monochorionic Diamniotic Twin Microvasculature and Placental Imaging

Summary

Twin-twin transfusion syndrome (TTTS) can arise in monochorionic, diamniotic (MoDi), those identical twins arising from division of a single fertilized ovum at 4-8 days gestational age (GA) or monochorionic, monoamniotic (MoMo or Mono-Mono) twins, arising from division on day 8-13 GA. In monochorionic twin pregnancies sharing a single placenta often unevenly, anastomoses \[connections\] artery to artery (AA), vein to vein (VV), and artery to vein (AV) can occur. AV anastomoses usually flow unilaterally, shunting blood unevenly towards one twin and away from the other. This can lead to fluid overload and polyhydramnios along with many other pathologies in one twin while the other twin suffers from inadequate blood flow and oligohydramnios, along with secondary pathologies arising from these conditions. TTTS will affect approximately 8-10% of MoDi twins while 6% of MoMo twins will suffer with this condition. Treatment for TTTS is necessary, with the donor or 'pump' twin having around an 80% chance of death without medical intervention. The aim of this single arm, unblinded, feasibility study of the Verasonics Vantage 256 device is to leverage the devices ultrafast power Doppler imaging (uPDI) to perform microvascular mapping of the placenta in healthy, non-anomalous, 18-26 week gestational age (GA), monochorionic, diamniotic (MoDi) or monochorionic, monoamniotic (MoMo/MonoMono) pregnancies without TTTS, twin reversed arterial perfusion sequence (TRAP), or maternal vascular disease. Participants will be recruited in the Maternal Fetal Medicine department of Carilion Clinic, which specializes in high risk or complicated pregnancies. Pregnant subjects carrying monochorionic twins and scheduled for appointments at the clinic, who meet study eligibility criteria, will be approached between weeks 18 and 26 for study enrollment. Those providing informed consent will undergo a single, transabdominal ultrasound examination by a licensed ultrasonographer or obstetrician with the Verasonics Vantage 256 ultrasound machine, with imaging focused on mapping the vasculature of the placenta with ultrafast power Doppler imaging (uPDI). The ultrasound exam will last about 15 minutes and occur immediately after the subject's standard-of-care appointment at the clinic so as not to inconvenience subjects more than necessary. Similar to commercially marketable ultrasounds in the US, the Verasonics ultrasound will use the principle of 'As Low As Reasonably Achievable (ALARA) to output the lowest acoustic waves possible to achieve the ultrasound imaging. After the single ultrasound scan, subjects' electronic medical records will be used to source demographic, medical, obstetric, and other historical datapoints to better characterize the 10-subject study population and their babies. No follow-up contact with subjects is expected after the single research ultrasound visit.