Which of the following is not a clinical criterion for diagnosing antiphospholipid syndrome?

Antiphospholipid syndrome (APS) is characterized by the presence of persistent antiphospholipid antibodies along with specific clinical criteria, primarily involving thrombosis and pregnancy complications. Among these criteria, vascular thrombosis is a well-established feature of APS, seen in various forms such as venous or arterial clots.

In terms of pregnancy outcomes associated with APS, the clinical criteria include specific types of pregnancy loss. A single fetal loss before 10 weeks of gestation associated with the presence of antiphospholipid antibodies serves as a noted criterion. However, preterm births in the absence of other risk factors or complications are not sufficient on their own to diagnose APS. The condition specifically outlines that there needs to be two or more pregnancy losses or particular complications, such as severe preeclampsia or fetal loss after 10 weeks, to qualify under its diagnostic criteria.

Thus, while two or more preterm births due to any reason can occur in a pregnant individual with APS, they do not meet the stringent criteria required for diagnosing the syndrome itself, distinguishing them from the more direct implications of conditions like severe preeclampsia or vascular thrombosis that are part of APS.