Porcine reproductive and respiratory syndrome virus (PRRSV) is transmitted vertically, causing fetal death in late gestation. Spatiotemporal distribution of virus at the maternal–fetal interface (MFI) is variable, and accurate assessment of viral concentration and lesions is thus subject to sampling error. Our objectives were: 1) to assess whether viral load and lesion severity in a single sample of endometrium (END) and placenta (PLC), collected near the base of the umbilical cord (the current standard), are representative of the entire organ; and 2) to compare sampling strategies and evaluate if spatial variation in viral load can be overcome by pooling of like-tissues. Spatially distinct pieces of END and PLC of 24 fetuses from PRRSV-2–infected dams were collected. PRRSV RNA quantified by RT-qPCR was compared in 5 individual pieces per fetus and in respective pools of tissue and extracted RNA. Three distinct pieces of MFI were assessed for histologic severity. Concordance correlation and kappa inter-rater agreement were used to characterize agreement among individual samples and pools. The viral load of individual samples and pools of END had greater concordance to a referent standard than did samples of PLC. Larger pool sizes had greater concordance than smaller pool sizes. Average viral load and lesion severity did not differ by location sampled, and no technical advantages of pooling tissues versus RNA extracts were found. We conclude that multiple pieces of MFI tissues must be evaluated to accurately assess lesion severity and viral load. Three pieces per fetus provided a reasonable balance of cost and logistic feasibility.

猪生殖和呼吸综合症病毒（PRRSV）垂直传播，导致妊娠后期胎儿死亡。母婴界面（MFI）上病毒的时空分布是可变的，因此对病毒浓度和病变的准确评估易受抽样误差的影响。我们的目标是：1）评估在脐带根部附近（当前标准）采集的子宫内膜（END）和胎盘（PLC）的单个样本中的病毒载量和病变严重程度是否代表整个器官；2）比较采样策略，评估是否可以通过合并类似组织来克服病毒载量的空间变化。收集了PRRSV-2感染大坝中24例胎儿的END和PLC在空间上不同的片段。通过RT-qPCR定量的PRRSV RNA在每个胎儿的5个独立片段中以及在各自的组织和提取的RNA中进行了比较。对MFI的三个不同部分进行了组织学严重性评估。一致性相关和kappa评价者之间的一致性被用来表征单个样本和库之间的一致性。与PLC样品相比，单个样品和END池的病毒载量与参考标准的一致性更高。较大的池大小比较小的池大小具有更大的一致性。平均病毒载量和病变严重程度在采样位置上没有差异，并且未发现与RNA提取物相比，合并组织的技术优势。我们得出结论，必须对多块MFI组织进行评估，以准确评估病变的严重程度和病毒载量。