TORONTO — Recurrent pregnancy loss was not associated with inherited maternal thrombophilias in a prospective study, adding weight to the evidence against screening for such disorders in patients presenting with a history of first-trimester miscarriage.
“It's probably more important to rule out other possible etiological factors,” said lead investigator Dr. Sony Sierra in an interview.
The study, which she presented at the annual meeting of the Society for Gynecologic Investigation, genotyped 915 Hutterite women for inherited thrombophilia polymorphisms including Factor V Leiden (FVL) Arg506Gln, the MTHFR Ala222Val, and the prothrombin G20210A variants. A total of 141 women were identified with inherited thrombophilias and were prospectively followed through 342 pregnancies.
The rate of fetal loss, defined as loss at or before 20 weeks of gestation, was 16% in the cohort, which is comparable to the rate found in the general population, reported Dr. Sierra, of the department of obstetrics and gynecology at the University of British Columbia in Vancouver.
“We also found that the majority of miscarriages occurred at less than 12 weeks—and since there has been evidence to suggest that thrombophilias could be associated with later fetal loss beyond 20 weeks, our findings just lend further support to the data that for early miscarriage there is no significant association,” she said.
Genotype analysis was performed on a subset of 72 live offspring and compared with maternal and paternal genotyping. The analysis revealed an expected transmission rate of the MTHFR Val allele to offspring; however, there were significantly fewer children born with the FVL allele (28) than expected (37). (There were no parental carriers of the prothrombin 20210A allele.)
“The significant deficit of children who inherit the FVL Gln allele from either heterozygous parent suggests that there may be preferential early loss of fetuses with this polymorphism,” said Dr. Sierra. “This unexpected result suggests selection against inherited thrombophilic variants during embryogenesis.”