Background/Purpose: AntiPhospholipid Syndrome Alliance For Clinical Trials and InternatiOnal Networking (APS ACTION) is an international research network created to conduct well-designed clinical trials in persistently antiphospholipid antibody (aPL)-positive patients. One of the first needs of APS ACTION was to know the true prevalence of aPL in the general population with pregnancy morbidity (PM).

Methods: The search for “aPL” and multiple keywords regarding the pregnancy outcomes of interest (early/late pregnancy loss [PrL], intrauterine growth restriction [IUGR], preeclampsia [PEC] and HELLP syndrome) was completed in PubMed. A total of 47 full-text papers were collected and analyzed for the type of outcome, the aPL tests used (criteria tests vs. non criteria), the definition of “positive aPL” (low, medium, high, other), the confirmation of aPL (at least 6-12 weeks apart), and the prevalence of positive aPL in the study population. The median prevalence and interquartile range (IQR) of different aPL tests were calculated based on the combine analysis of all the papers.

 Results: Out of 47 papers, the outcome of interest was PrL in 32 (68%), IUGR in 6 (13%), PEC in 20 (42%), and/or HELLP syndrome in 6 (13%). Despite the limitations of the literature, the table demonstrates the estimated aPL prevalence in patients with different type of PM. These limitations were: a) the definition of  “pregnancy outcome” was  highly heterogeneous (66% of the studies did not define the PrL based on the Updated Sapporo Criteria; 31% did not specify the number and/or the gestational week of the PrL; 47% of the early PrL studies included patients with less than 3 events; and 85% included patients with events before and after 10 weeks in the same analysis); b) nomenclature of late PrL was controversial due to the overlap between terms such as abortion, intrauterine fetal death, and stillbirth; fetal malformations were rarely excluded (36%); c) IUGR was defined as <5^th percentile in 33% of the studies and <10^th percentile in 50%; 17% of the papers included no cut-off values; d) PEC severity was identified only in 50% of the studies; e) the numbers of patients included in all studies were relatively small (median 70; IQR 29-162); f) aPL type (6%) or isotype (32%) has not been specified in 38% of the studies; g) aCL and/or aβ2GP-I ELISA cut-off was not available in 11% of the studies and “low titer” (<20U) was used in 21% of the papers; and h) the confirmation of aPL was performed only in 9 studies (19%).

Conclusion: The current best estimates of aPL prevalence in patients with PM are impaired by several limitations of the literature including the definition of obstetric outcomes and “positive aPL”. One of the goals of APS ACTION is to improve upon existing literature in order to address the precise magnitude of the problem.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-estimated-prevalence-of-antiphospholipid-antibodies-in-the-general-population-with-pregnancy-morbidity/