Study shows 1 in 4 preemies are born with fetal bacteremia. Premature babies are subject to a host of threats that can result in fetal/neonatal disease. Researchers have found that genital mycoplasmas are a frequent cause of congenital fetal infection. 23 percent of neonates born between 23 and 32 weeks of gestation have positive umbilical blood cultures for two genital mycoplasmas (bacteria lacking cell walls): Ureaplasma urealyticum and Mycoplasma hominis.