Introduction: The ‘sterile womb paradigm’ is currently under debate and the advent of next generation 16S rRNA gene sequencing is driving the characterization of microbes associated with the amniotic cavity during pregnancy.

Objective: To characterize the bacterial diversity in placentas from preterm and term births using next generation 16S rRNA gene sequencing in association with adverse pregnancy outcomes and histopathology studies.

Methods: In this prospective study, placentas were collected consecutively from patients attending a public tertiary referral hospital in South Africa, delivering preterm (n=42; 28-34 weeks gestational age) and term (n=20; >37 weeks gestational age). Placentas underwent histopathology tests and next generation 16S rRNA gene sequencing.

Results: Analysis of microbial diversity in the placenta showed a significantly higher alpha diversity in term placentas compared to preterm placentas (P=0.000075), in placentas with acute chorioamnionitis compared to placentas without acute chorioamnionitis (P=0.0061), between HIV negative term births and both HIV negative and HIV positive preterm births (P=0.0118 and P=0.0008), respectively. Beta diversity was significantly different between preterm and term births (unweighted UniFrac distance, P=0.003996; Jaccard distance, P=0.03696) and Escherichia/Shigella, Shuttleworthia, Anaeroglobus and Megasphaera were differentially expressed.

Conclusion: This is the first South African study to characterize the bacterial diversity in placentas from complicated pregnancies using next generation 16S rRNA gene sequencing in conjunction with full placental histology. Microbial diversity differs between preterm and term placentas where HIV may act as a cofactor associated with decreased bacterial alpha diversity in placentas from preterm birth. 

Next generation sequencing, 16S rRNA, Placenta, Preterm birth, HIV, Acute chorioamnionitis