Late Fetal Loss (>10 weeks) is the Most Common Fetal Manifestation Alerting to APS
Late fetal loss occurring at or after 10 weeks' gestation is the most characteristic and common fetal manifestation that alerts clinicians to the possibility of Antiphospholipid Syndrome (APS). 1
Clinical Criteria for Obstetric APS
The 2020 American College of Rheumatology guidelines clearly define the obstetric manifestations that meet criteria for APS diagnosis 1:
- One or more unexplained fetal deaths at or after 10 weeks' gestation (most typical presentation) 1
- Three or more consecutive pregnancy losses before 10 weeks' gestation 1
- One or more premature births before 34 weeks due to severe preeclampsia, intrauterine growth restriction, or placental insufficiency 1
Why Late Fetal Loss is Most Characteristic
Fetal deaths beyond the 10th week of gestation represent the most typical obstetric complication of APS 2. This distinguishes APS from other causes of pregnancy loss:
- Late pregnancy losses are relatively uncommon in the general population, making them a more specific indicator of underlying pathology 3, 4
- The pathophysiology involves defective endovascular decidual trophoblastic invasion and placental thrombosis, which manifests more prominently in later pregnancy 3
- Research on anti-phosphatidylserine/prothrombin antibodies confirms these antibodies are more prevalent and show higher titers in patients with late pregnancy loss compared to early pregnancy loss 1
Distinguishing Features by Gestational Age
Early vs. Late Losses:
- Early losses (<10 weeks) require three consecutive losses to meet APS criteria, as early miscarriage is common in the general population 1
- Late losses (≥10 weeks) require only one unexplained loss to meet criteria, reflecting their greater specificity for APS 1
Other Obstetric Manifestations
While late fetal loss is most characteristic, clinicians should remain alert to other APS-related complications 1:
- Severe preeclampsia occurring before 34 weeks 1
- Premature birth before 34 weeks due to placental insufficiency or fetal distress 1
- Intrauterine growth restriction 1
These complications occur in approximately 50% of APS patients despite treatment 5, but they are less specific initial presentations than late fetal loss.
Clinical Implications
When to suspect APS:
- Any unexplained fetal death at or after 10 weeks should prompt aPL testing 1
- Testing should include lupus anticoagulant, anticardiolipin antibodies (IgG and IgM), and anti-β2-glycoprotein I antibodies (IgG and IgM) 1
- Positive results must be confirmed with repeat testing at least 12 weeks apart 1
Answer: B. Late fetal loss (>10 weeks) is the correct answer, as it represents the single most characteristic obstetric manifestation that alerts providers to possible APS 1, 2.