Caracteristics of women presenting with Chronic Histiocytic Intervillositis during pregnancy: a case-control study.

Introduction: Chronic Histiocytic Intervillositis (CHI) appears to be among the most severe placental diseases. Its rarity has limited our knowledge of the women in whom it occurs.

Objective: To search for maternal characteristics linked to the existence of CHI, by first studying the current pregnancy included in the study, then their previous pregnancies.

Material and methods: We conducted a monocentric case-control study between 2000 and 2020. CHI cases were diagnosed by microscopic examination of the placenta. "Low-risk" controls gave birth just before each case, whatever the outcome. "High-risk" controls benefited from placental microscopy immediately after the case examinations.

Results: 151 women were included in each group. CHI cases had twice as many previous pregnancies as both controls, but no more living children at home. Regarding obstetric history, fetal losses were significantly higher in CHI cases: compared to "low-risk" controls, there were more early miscarriages (20.0%, OR 2.6 [1.5;4.8]), late miscarriages (4.8%, OR 8.8 [1.1;187]) and in utero deaths (5.4%, OR 5.6 [1.7;19.8]). The risk of fetal loss does not appear to be increased in first pregnancies of CHI cases. However, differences appeared between cases and both "low-risk" and "high-risk" controls with a history of two previous miscarriages (21.7% vs 11.2%, p=0.009 or vs 9.6%, p=0.005) and the outcome of the second pregnancy (number of living children 59.7% vs 78.0%, p=0.033 or vs 63.0%, p=0.71), respectively.

Conclusion: Women with CHI have a more frequent history of pregnancy failure than other women. This excess fetal loss seems to occur only after the second pregnancy or after two previous miscarriages.