Fetal haemodynamic assessment in a case of late-onset intrauterine growth restriction by phase contrast MRI and T2 mapping
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KeywordsPulsatility Index Umbilical Artery Fetal Weight Late Gestation Placental Insufficiency
Late-onset intrauterine growth restriction (IUGR) results from the failure of placenta to supply enough nutrients and oxygen to the rapidly growing late gestation fetus . Inaccuracies in ultrasound based late gestational fetal weight estimation and the absence of typical Doppler changes make late-onset IUGR difficult to detect . We were interested in whether new MRI technology incorporating fetal vessel blood flow and oximetry measurement could improve the sensitivity of conventional fetal monitoring.
A normal pregnancy was studied at late gestation as part of an IRB approved study. The pulsatility index (PI) in the umbilical artery (UA) and middle cerebral artery (MCA) were measured using Doppler ultrasound. At 34, 36 and 39 week's gestational age (GA), MRI scans were performed using a 1.5T Siemens Avanto. We measured fetal weight (3D SSFP), the flow and oxygen saturations in the major fetal vessels using phase contrast MRI and T2 mapping according to our previously published technique . Fetal oxygen delivery (DO2) and consumption (VO2) were calculated using a haemoglobin concentration taken from population averages . We also recorded clinical fetal monitoring and placental histopathology results.
The fetal weight centile decline, placental histology and small for gestational age birth-weight in this case are in keeping with late-onset IUGR. We propose that the drop in fetal oxygen delivery is evidence of placental insufficiency while the dropped oxygen consumption is in keeping with fetal metabolic adaptation to reduced oxygen delivery, which resulted in slowing of fetal growth. With this novel approach to fetal hemodynamics, MRI could provide clinically significant additional information to conventional fetal monitoring.
Canadian Institute of Health Research/Sickkids Foundation New Investigator Award.
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