The change of fetal heart rate short-term variability during the course of histological chorioamnionitis in fetal sheep.

Objective: Histological chorioamnionitis (CAM) is related to neonatal mortality and morbidity. However, identifying intrauterine inflammation before delivery is challenging. The aim of this study was to investigate the changes in fetal heart rate (FHR) short-term variability (STV) during the course of histological CAM.

Study Design: Changes in STV were measured in 7 chronically instrumented fetal sheep at 111-120 days of gestation. Lipopolysaccharide (LPS) was infused into the amniotic cavity for 2 days following the 4th postoperative day to develop histological CAM. STV was determined based on the R to R interval of the fetal electrocardiogram. We continued to observe the changes in STV until the time of intrauterine fetal death (IUFD). The umbilical cord and fetal membranes were evaluated histologically after IUFD. The experiment was divided into two phases: 1) the acute phase, defined as the 24-hour period between the first and second injections of LPS and 2) the perimortem phase, defined as the period between the second injection of LPS and IUFD. Changes in STV in both the acute and perimortem phases were evaluated using Friedman's test. A probability of <0.05 was accepted as statistically significant.

Results: The fetuses died, on average, at 23.7 ± 4.9 h after the second injection of LPS. Both the umbilical cord and fetal membranes showed histological evidence of severe inflammation. During the perimortem phase, there were statistically significant differences in STV at each time point. STV increased significantly at 6, 4, and 3 h before intrauterine fetal death compared to the baseline.

Conclusion: Our study suggests that STV increased as the fetal condition deteriorated during the course of histological CAM.