Are early pregnancies implanted close to the tubal ostia at increased risk of miscarriage? A prospective observational study

Introduction: The aim of this article is to assess any association between the risk of miscarriage and the distance of an early pregnancy from the closest tubal ostia.

Methods: Early pregnancy was defined as a gestational sac ⩽ 15 mm mean diameter within the upper half of the endometrial cavity. The shortest distance from the gestational sac (chorionic membrane) to the closest tubal ostia and the interostial distance were measured. The outcomes for pregnancies at varying distances from a tubal ostia were compared using Fisher's exact test. The receiver operating characteristic curve assessed the distance from the sac to the ostia as a predictor of miscarriage. A Wilcoxon rank-sum test was used to assess any difference in the distance from the ostia between women who miscarried and those who did not.

Results: Outcome data were available for 212/230 patients. The relative risk of miscarriage was 5/6 (83%) in the group with gestational sacs ⩽ 4 mm from the ostium versus 70/206 (34%) > 4 mm (p = 0.02). The proportion of miscarriages was 11/20 (55%) if the distance from the tubal ostium was ⩽5 mm versus 64/192 (33%) if >5 mm (p = 0.08). There was a good neonatal outcome for those with live births.

Conclusion: The risk of first trimester miscarriage was high with early pregnancies implanted close to the tubal ostia, but this finding did not reach statistical significance. A larger study is needed to establish whether 4 or 5 mm could be used as a clinically useful criterion for defining early pregnancies that are at increased risk of miscarriage.