The infrequent occurrence of mycoplasmas in amniotic fluid from women with intact fetal membranes.

As human genital mycoplasmas have been associated with various forms of reproductive failure, the present study was undertaken to investigate whether M. hominis and U. urealyticum organisms (ureaplasmas) are capable of crossing intact fetal membranes. Nearly 300 women in Denmark and England were investigated. Most of them were seen at about the fourth month of gestation and the remainder towards or at the time of birth, all with unruptured membranes. A swab was taken from the uterine cervix or vagina and M. hominis was isolated from 9% of the women and ureaplasmas from half of them. The presence of these mycoplasmas was not associated with an abnormal outcome of pregnancy. In contrast to the frequent presence of mycoplasmas in the lower genital tract, amniotic fluids obtained by transabdominal amniocentesis or at cesarean section did not contain M. hominis and ureaplasmas were isolated from only one of them. This was associated with the same ureaplasmas serotype being recovered from the cervix and also from the blood of both infant and mother, whose case differed from the others as labor had already started when the amniotic fluid was obtained. Thus, in our populations, we have no evidence that mycoplasmal invasion of the amniotic fluid occurs before the onset of labor. During labor, despite intact membranes, it seems that genital mycoplasmas may occasionally invade the fetal--placental unit, probably by the hematogenous route after strong uterine contractions, or otherwise directly after membrane rupture. Since both these events are followed usually by immediate delivery, there would seem to be insufficient time for the genital mycoplasmas to cause fetal damage.