Chronic villitis of unknown aetiology in placentae of idiopathic small for gestational age infants.

Placentae from 63 term pregnancies were studied. Of these, 19 were from normal pregnancies in which the neonates were within the normal weight range for their gestational age. The remaining 44 placentae were from pregnancies in which the infants were small for their gestational age (SGA). A chronic villitis was found in 68 per cent of all placentae. In the control group this lesion was present in 26 per cent but a mean of only 1.2 per cent of villi in these cases was inflamed. In the SGA group 86 per cent of placentae showed a chronic villitis and in these an average of 10 per cent of the villi were inflamed. Lymphocytic infiltrates in basal plate anchoring villi were observed in 48 of the 63 placentae and there were no differences among the various groups. Vascular lesions were found, similar to those described in placental bed arteries in preeclampsia and more recently in biopsies of the placental bed of SGA infants and in the decidua of mothers with systemic lupus erythematosus: this type of vasculopathy has also been described in rejection of renal transplants. It is suggested that the cellular infiltrate around and inside anchoring villi and free villi in cases of chronic villitis may represent the histological hallmark of an immunological reaction between mother and fetus rather than a response to infection.