A primary study: high-throughput sequencing analysis of amniotic fluid microbiota in 50 high-risk pregnant women during the second trimester

Objective: Whether bacteria exist in the pregnancy uterus without pathological infection has long been a controversial topic. Through this study, we aim to determine whether characteristic amniotic fluid microbiota exists in the uterus of high-risk pregnant women during the second trimester. Methods: This study recruited high-risk pregnant women in the second trimester from September 1, 2024, to August 30, 2025, and recorded their age and gestational age. Amniotic fluid samples were obtained through amniocentesis under strictly sterile conditions, and 16S rRNA high-throughput sequencing was performed on the samples. The inclusion criteria mainly consisted of: advanced maternal age, non-invasive prenatal test results indicating chromosomal abnormalities, abnormal fetal ultrasound findings, history of adverse pregnancy outcomes, and high-risk Down syndrome screening results. Results: differed between the two groups. A slight difference in microbiota diversity was observed between women with gestational ages below 20 weeks and those at 20 weeks or above, but no significant difference was found in microbial composition between the two groups. Conclusion: being the predominant phyla, showing limited correlation with maternal age or gestational age. This study provided evidence for the presence of microorganisms in amniotic fluid during pregnancy and might offer some preliminary data for future research related to eugenics and reproductive health.