What is the best time to assess the antiphospholipid antibodies (aPL) profile to better predict the obstetric outcome in antiphospholipid syndrome (APS) patients?

Serological risk factors are the most important determinant in predicting unsuccessful pregnancy in obstetric antiphospholipid antibodies syndrome (OAPS) despite conventional treatment. It is not clear if changes in the profile of antiphospholipid antibodies (aPL) during pregnancy modify the risk associated with a poor response to conventional treatment. The aim of our study was to compare the value of a serological tag for aPL obtained before and during the first trimester of pregnancy to predict the response to conventional treatment. We carefully selected 97 pregnancies in women who were included in our study only if they were diagnosed with OAPS prior to a new pregnancy (basal serological risk), retested for aPL during the first trimester of pregnancy (serological risk during pregnancy), and treated with conventional therapy. High baseline serological risk was associated with pregnancy failure in 62.1% of cases (18/29) and predicted 82.5% of pregnancy outcomes with conventional treatment: OR = 16.9, CI = 5.5-52.1, p < 0.001. High serological risk during pregnancy was associated with pregnancy failure in 86.3% of cases (19/22) and predicted 91.8% of pregnancy outcomes with conventional treatment: OR = 88.7, CI = 19.4-404.8, p < 0.001. According to these results, we found that risk categorization performed during pregnancy was better in predicting pregnancy outcome (82.5 vs. 91.8%). Moreover, risk categorization during pregnancy had an increased specificity regarding the prediction: 84.9% at baseline and 95.9% during pregnancy (p = 0.024). Our findings suggest that it is important to perform aPL during the first trimester of pregnancy since that is the best time to establish the serological risk factors.