Objective Transperitoneal transmigration of sperm constitutes the mechanism by which ectopic pregnancies occur in unilaterally obstructed fallopian tubes. This study was undertaken to determine how often sperm transmigrate across the peritoneal cavity to effect human pregnancy. Design In women with non-communicating rudimentary uterine horn pregnancies, the ratio of total uterine horn pregnancies to prior contralateral hemi-uterine pregnancies was calculated to infer the overall transperitoneal sperm transmigration rate. The prior parity frequency distribution was also determined to calculate the best-fit per-pregnancy probability of attaining a rudimentary horn pregnancy with each subsequent gestation using maximum likelihood estimation. Setting 20th century. Sample Non-communicating rudimentary uterine horn pregnancies reported from 40 countries. Methods Two hundred and seventy-two cases were identified using manual and computerised searches of Index Medicus, Excerpta Medica, the Index-Catalogue of the Library of the Surgeon-General's Office and standard reference tracing. Main outcome measures The ratio of total prior non-rudimentary uterine horn pregnancies to rudimentary uterine horn pregnancies and the frequency distribution of prior maternal parities. Results Prior to the incident 272 uterine horn pregnancies, the number of observed pregnancies was 292 (ratio = 0.93), implying an aggregate sperm transmigration rate of 0.48. Using the prior parity frequency distribution, the best-fit probability of attaining a rudimentary horn gestation per-pregnancy was 0.51 (95% CI 0.48-0.56). Conclusions Intraperitoneal sperm transmigration occurs approximately half the time in effecting spontaneous human pregnancies. To minimise the risk of ectopic tubal pregnancy in woman with unilaterally damaged fallopian tubes, salpingectomy should be the preferred surgical treatment, rather than attempting tubal salvage and repair.
