The Fetal Spleen in Low-Risk Pregnancies and prior to Preterm Birth: Observational Study of the Role of Anatomical and Functional Magnetic Resonance Imaging

Abstract

<b><i>Introduction:</i></b> Spontaneous preterm birth complicates ∼7% of pregnancies and causes morbidity and mortality. Although infection is a common etiology, our understanding of the fetal immune system in vivo is limited. This study aimed to utilize T2-weighted imaging and T2* relaxometry (which is a proxy of tissue oxygenation) of the fetal spleen in uncomplicated pregnancies and in fetuses that were subsequently delivered spontaneously prior to 32 weeks. <b><i>Methods:</i></b> Women underwent imaging including T2-weighted fetal body images and multi-eco gradient echo single-shot echo planar sequences on a Phillips Achieva 3T system. Previously described postprocessing techniques were applied to obtain T2- and T2*-weighted imaging of the fetal spleen and T2-weighted fetal body volumes. <b><i>Results:</i></b> Among 55 women with uncomplicated pregnancies, an increase in fetal splenic volume, splenic:body volume, and a decrease in splenic T2* signal intensity was demonstrated across gestation. Compared to controls, fetuses who were subsequently delivered prior to 32 weeks’ gestation (<i>n</i> = 19) had a larger spleen when controlled for the overall size of the fetus (<i>p</i> = 0.027), but T2* was consistent (<i>p</i> = 0.76). <b><i>Conclusion:</i></b> These findings provide evidence of a replicable method of studying the fetal immune system and give novel results on the impact of impending preterm birth on the spleen. While T2* decreases prior to preterm birth in other organs, preservation demonstrated here suggests preferential sparing of the spleen.