Several aspects of placental structure may be altered in fetal growth restriction (FGR). MRI provides quantitative indices that relate to tissue structure, including relaxation time measurements, T1 and T2. The authors hypothesised these can be used as biomarkers to identify alterations in placental tissue structure and therefore be a useful means of non-invasive placental assessment, particularly in FGR. Here, the authors report on the first phase of testing this hypothesis, in women with normal pregnancies.
Aim To assess placental relaxation time measurements and correlate these with gestational age and stereological analyses following delivery.
Methods 22 women underwent MRI examination (1.5 T) between 20- and 41-week gestation. T1 and T2 measurements were acquired for a whole placental image. Placental biopsies were sampled systematically and subjected to stereological analysis.
Results Linear regression analysis showed the following, in keeping with studies at 0.5 T.
T1=696+(2.1-week gestation), r2=0.15, p=0.09
T2=254+(19.6-week gestation), r2=0.15, p=0.10
10 term placentas and a subgroup of five from pregnancies all scanned at 36 weeks were analysed. Although no significant correlations were demonstrated, trends were observed showing longer relaxation times with increasing villous and fibrin volume and ratio of fibrin:villous tissue. An increase in fetal capillary volume, capillary surface area and ratio of capillary:villous tissue, were all associated with a fall in T1 and increase in T2.
Discussion FGR is associated with impoverished villous development and reduction in fetal capillary volume. Our data suggest relaxation times may be a useful non-invasive biomarker of placental variables and potentially useful in identifying FGR in utero.
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