Serum microRNAs are promising novel biomarkers for clinical diagnosis. This study demonstrates that microRNAs, small non-coding regulatory RNAs involved in human development and disease, are present in bodily fluids and can serve as effective biomarkers. The researchers developed protocols for extracting and quantifying microRNAs in serum and other body fluids, validating the robustness of their methods. They compared serum microRNA levels in pregnant and non-pregnant women, finding that microRNAs associated with the human placenta were significantly elevated in pregnant women, correlating with pregnancy stage. The study highlights the potential of microRNAs as clinically relevant biomarkers due to their stability in body fluids and their ability to reflect physiological and pathological conditions. The researchers demonstrated that microRNA levels in serum can be used to detect changes in physiological states, such as pregnancy. They also showed that microRNAs are stable during freeze-thaw cycles, making them suitable for clinical use. The study further shows that microRNAs are present in various body fluids, including serum, urine, saliva, amniotic fluid, and pleural fluid. The microRNA profiles of these fluids reflect physiological conditions, with serum microRNA levels differing between pregnant and non-pregnant women. Specifically, three placental microRNAs (hsa-miR-526a, hsa-miR-527, and hsa-miR-520d-5p) were found to be significantly elevated in pregnant women and could be used to distinguish pregnant from non-pregnant women. The study also found that certain microRNAs, such as hsa-miR-141 and hsa-miR-149, are associated with epithelial tissues and show increased abundance during pregnancy. These findings support the potential of microRNAs as biomarkers for various diseases, including preeclampsia, a common complication of pregnancy. The study concludes that microRNAs are a new class of circulating nucleic acids with significant potential as clinical biomarkers for diverse physiological and pathological conditions.Serum microRNAs are promising novel biomarkers for clinical diagnosis. This study demonstrates that microRNAs, small non-coding regulatory RNAs involved in human development and disease, are present in bodily fluids and can serve as effective biomarkers. The researchers developed protocols for extracting and quantifying microRNAs in serum and other body fluids, validating the robustness of their methods. They compared serum microRNA levels in pregnant and non-pregnant women, finding that microRNAs associated with the human placenta were significantly elevated in pregnant women, correlating with pregnancy stage. The study highlights the potential of microRNAs as clinically relevant biomarkers due to their stability in body fluids and their ability to reflect physiological and pathological conditions. The researchers demonstrated that microRNA levels in serum can be used to detect changes in physiological states, such as pregnancy. They also showed that microRNAs are stable during freeze-thaw cycles, making them suitable for clinical use. The study further shows that microRNAs are present in various body fluids, including serum, urine, saliva, amniotic fluid, and pleural fluid. The microRNA profiles of these fluids reflect physiological conditions, with serum microRNA levels differing between pregnant and non-pregnant women. Specifically, three placental microRNAs (hsa-miR-526a, hsa-miR-527, and hsa-miR-520d-5p) were found to be significantly elevated in pregnant women and could be used to distinguish pregnant from non-pregnant women. The study also found that certain microRNAs, such as hsa-miR-141 and hsa-miR-149, are associated with epithelial tissues and show increased abundance during pregnancy. These findings support the potential of microRNAs as biomarkers for various diseases, including preeclampsia, a common complication of pregnancy. The study concludes that microRNAs are a new class of circulating nucleic acids with significant potential as clinical biomarkers for diverse physiological and pathological conditions.