The fetal spleen in low-risk pregnancies and prior to preterm birth: Observational study of the role of anatomical and functional MRI.

Introduction Spontaneous preterm birth complicates ~7% of pregnancies and causes morbidity and mortality. Although infection is a common aetiology, our understanding of the fetal immune system in vivo is limited. This study aimed to utilise T2 weighted imaging and T2* relaxometry (which is a proxy of tissue oxygenation) of the fetal spleen in uncomplicated pregnancies, and in fetuses that subsequently deliver spontaneously prior to 32 weeks. Methods 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. Results 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 subsequently delivered prior to 32 weeks' gestation (n=19) had a larger spleen when controlled for the overall size of the fetus (p=0.027), but T2* was consistent (p=0.76). Conclusion 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.