650 Stability of placental mRNA expression within 24 hours of delivery

Abstract

Current guidelines recommend collecting placental specimens within two hours of delivery for gene expression analysis. However, collecting samples in a narrow time window is a challenge in the dynamic and unpredictable clinical setting of Labor and Delivery units, so delays in placental specimen collection are possible. The purpose of our analysis is to investigate temporal changes in placental gene expression by longitudinally sampling placentas over a 24-hour period. Placentas from 8 individuals with uncomplicated, term pregnancies delivered by scheduled cesarean section were collected and sampled immediately following delivery and again 1, 2, 4, 6, and 24-hours post-delivery. At each timepoint, biopsies of chorionic villous tissue were taken from 3 cotyledons to account for intra-placental heterogeneity. The 3 biopsies from each timepoint were pooled prior to RNA extraction. Expression of 364 mRNA transcripts was quantified using the nanoString nCounter system. Fold change values were calculated for each timepoint relative to delivery and a fold-change threshold of 1.25 was used to determine a meaningful change from delivery. A majority of transcripts (61%) were stable through 4 hours and 80% were stable for at least 2 hours (Figure 1). Eight expression patterns were identified (Figure 2). Three patterns (25% of transcripts) reflect a trend of increasing expression relative to delivery, four patterns (35%) reflect a trend of decreasing expression, and one pattern reflects no change in expression (21%). The remaining 19% of transcripts were variable over time, such that no consistent pattern emerged. We have also developed an app to allow investigators to explore study data pertinent to their research (https://placentaexpression.foundationsofhealth.org/). Our results confirmed that samples collected within 2 hours have the most stable gene expression, but many transcripts are stable through 4 hours, and some through 24 hours. Depending on the transcripts and biologic pathways of interest, it may not be necessary to exclude specimens with delayed collection.View Large Image Figure ViewerDownload Hi-res image Download (PPT)