A study by Susanne Lager (Obstetrics and Gynaecology) and Marcus de Goffau (Veterinary Medicine and Wellcome Sanger Institute), led by Steve Charnock-Jones and Gordon Smith (both Obstetrics and Gynaecology), showed, conversely to other studies, that the placenta does not have a microbiome.

The placenta is the critical interface between the mother and the growing foetus, transporting nutrients and waste and proving a barrier to protect the foetus from the maternal immune system and infections. Many of the causes of adverse pregnancy outcome are due to perturbation of placental function, so reports claiming that the placenta harboured a microbiome were potentially of great importance.

Published in Nature, this collaborative study analysed more than 500 samples collected from pregnant women recruited to the NIHR-funded Pregnancy Outcome Prediction (POP) study. The work demonstrated no evidence of bacteria in the large majority of placental samples, from both complicated and uncomplicated pregnancies. The only exception was the presence of Group B Streptococcus (GBS) found in the placenta in about 5% of women prior to the onset of labour. GBS is the major cause of sepsis in newborns and approximately 150,000 babies die each year in the world because of GBS sepsis. Although many of these are in low and middle income countries, in the UK about 50 babies die each year and 20-30 are suffer lifelong impairment as a result of GBS sepsis. This study indicates that the baby may be exposed to the bacterium in the womb rather than following rupture of the foetal membranes during labour and delivery, so the next steps include studying the relationship between the presence of GBS in the placenta and the risk of sepsis following birth. If a link is established, development of methods to test the placenta following delivery may allow targeting of antibiotics to prevent baby deaths due to sepsis.

Reference:

de Goffau MC, Lager S, Sovio U, Gaccioli F, Cook E, Peacock SJ, Parkhill J, Charnock-Jones DS and Smith GCS (2019). Human placenta has no microbiome but can contain potential pathogens. Nature 572(7769): 329-334