Quantifying circulating hypoxia-induced RNA transcripts in maternal blood to determine in utero fetal hypoxic status.

BACKGROUND: Hypoxia in utero can lead to stillbirth and severe perinatal injury. While current prenatal tests can identify fetuses that are hypoxic, none can determine the severity of hypoxia/acidemia. We hypothesized a hypoxic/acidemic fetus would up-regulate and release hypoxia-induced mRNA from the fetoplacental unit into the maternal circulation, where they can be sampled and quantified. Furthermore, we hypothesized the abundance of hypoxia induced mRNA in the maternal circulation would correlate with severity of fetal hypoxia/acidemia in utero. We therefore examined whether abundance of hypoxia-induced mRNA in the maternal circulation correlates with the degree of fetal hypoxia in utero. METHODS: We performed a prospective study of two cohorts: 1) longitudinal study of pregnant women undergoing an induction of labor (labor induces acute fetal hypoxia) and 2) pregnancies complicated by severe preterm growth restriction (chronic fetal hypoxia). For each cohort, we correlated hypoxia induced mRNA in the maternal blood with degree of fetal hypoxia during its final moments in utero, evidenced by umbilical artery pH or lactate levels obtained at birth. Gestational tissues and maternal bloods were sampled and mRNAs quantified by microarray and RT-PCR. RESULTS: Hypoxia-induced mRNAs in maternal blood rose across labor, an event that induces acute fetal hypoxia. They exhibited a precipitous increase across the second stage of labor, a particularly hypoxic event. Importantly, a hypoxia gene score (sum of the relative expression of four hypoxia-induced genes) strongly correlated with fetal acidemia at birth. Hypoxia-induced mRNAs were also increased in the blood of women carrying severely growth restricted preterm fetuses, a condition of chronic fetal hypoxia. The hypoxia gene score correlated with the severity of ultrasound Doppler velocimetry abnormalities in fetal vessels. Importantly, the hypoxia gene score (derived from mRNA abundance in maternal blood) was significantly correlated with the degree of fetal acidemia at birth in this growth restriction cohort. CONCLUSIONS: Abundance of mRNAs coding hypoxia-induced genes circulating in maternal blood strongly correlates with degree of fetal hypoxia/acidemia. Measuring hypoxia-induced mRNA in maternal blood may form the basis of a novel non-invasive test to clinically determine the degree of fetal hypoxia/acidemia while in utero.

Quantifying mRNA coding growth genes in the maternal circulation to detect fetal growth restriction.

OBJECTIVE: To examine whether mRNA circulating in maternal blood coding genes regulating fetal growth are differentially expressed in (1) severe preterm fetal growth restriction (FGR) and (2) at 28 weeks' gestation in pregnancies destined to develop FGR at term. STUDY DESIGN: mRNA coding growth genes were measured in 2 independent cohorts. The first was women diagnosed with severe preterm FGR (<34 weeks' gestation; n = 20) and gestation matched controls (n = 15), where the mRNA was measured in both maternal blood and placenta. The second cohort was a prospective longitudinal study (n = 52) of women whom had serial ultrasound assessments of fetal growth. mRNA coding growth genes in maternal blood were measured at 28 and 36 weeks in pregnancies with declining growth trajectories (ending up with term FGR; n = 10 among the 52 recruited) and controls who maintained normal growth trajectory (n = 15). RESULTS: In women with severe preterm FGR, there was increased expression of placental growth hormone (6.3-fold), insulin-like growth factors (IGF1, 3.4-fold; IGF2, 5.0-fold), IGF receptors (2.1-fold) and IGF binding proteins (3.0-fold), and reduced expression of ADAM12 (0.5-fold) in maternal blood (and similar trends in placenta) compared with controls (P < .05). Notably, at 28 weeks' gestation there was increased IGF2 (3.9-fold), placental growth hormone (2.7-fold), and IGF BP2 (2.1-fold) expression in maternal blood in women destined to develop FGR at term (P < .05). CONCLUSION: Measuring mRNA coding growth genes in maternal blood may detect unsuspected severe preterm FGR already present in utero, and predict term FGR when measured at 28 weeks' gestation.

Placental specific mRNA in the maternal circulation are globally dysregulated in pregnancies complicated by fetal growth restriction.

CONTEXT: Fetal growth restriction (FGR) is a leading cause of perinatal mortality, yet no reliable screening test exists. Placental specific mRNA in the maternal circulation may reflect changes in the placental transcriptome in FGR and could be a novel biomarker for FGR. OBJECTIVE: The aim of the study was to identify placental specific RNA detectable in the maternal circulation and examine whether they are differentially expressed in severe preterm FGR. DESIGN: In silico screening was used to identify placental specific RNAs. Their expression in cases of severe FGR vs controls was examined in both maternal blood and placenta by microarray, RT-PCR, and in situ hybridization. RESULTS: Via in silico analysis, we identified 137 genes very highly expressed in the placenta relative to other tissues. Using microarray, we found that they were detectable in the maternal blood and were globally dysregulated with preterm FGR; 75 genes (55%) had a ≥1.5-fold differential expression compared to controls. Eight genes (ERVWE-1, PSG1, PLAC4, TAC3, PLAC3, CRH, CSH1, and KISS1) were validated by RT-PCR to be significantly increased in both maternal blood and placenta in a larger cohort of severe FGR compared to controls. In situ hybridization confirmed PAPPA2 and ERVWE-1 localized to the syncytiotrophoblast. CONCLUSION: There is global differential expression of placental specific mRNA in the maternal blood in pregnancies complicated by severe preterm FGR. Placental specific mRNA in maternal blood may represent a new class of biomarkers for preterm FGR.