Best Initial Blood Investigation for Recurrent Spontaneous Abortion and Delayed Conception
The best initial blood investigation is antiphospholipid antibody testing (anticardiolipin antibodies, anti-β2 glycoprotein I antibodies, and lupus anticoagulant), followed by thyroid function tests (TSH, thyroid peroxidase antibodies, thyroglobulin antibodies). 1
Primary Testing Panel
The most recent guideline evidence 1 and supporting research 2 establish a clear hierarchy for initial workup:
First-Line Essential Tests:
Antiphospholipid Syndrome (APS) Screening:
- Anticardiolipin antibodies (IgG and IgM)
- Anti-β2 glycoprotein I antibodies (IgG and IgM)
- Lupus anticoagulant testing
This is the single most important treatable cause of RSA, with strong guideline support 3, 1. The 2025 Canadian guideline specifically recommends screening for antiphospholipid syndrome as a priority 1, and the 2017 EULAR recommendations emphasize APS management in pregnancy 3.
Thyroid Function:
- TSH
- Thyroid peroxidase antibodies (TPO-Ab)
- Thyroglobulin antibodies (TG-Ab)
Meta-analysis confirms significantly elevated thyroid antibodies in RSA patients 2, and the 2025 guideline explicitly recommends thyroid dysfunction screening 1.
Secondary Testing Based on Clinical Context
Autoimmune Markers (if APS testing suggests broader autoimmune disease):
- Antinuclear antibody (ANA) - shows the highest correlation with RSA (R = 0.612) 2
- Anti-double-stranded DNA antibody (if ANA positive)
- Complement levels (C3, C4) - particularly important for monitoring if SLE suspected 3
Coagulation Parameters (if thrombophilia suspected):
- Protein S activity (significantly decreased in RSA) 2, 4
- Protein C activity 2
- Antithrombin III 4
- D-dimer 4
The combined use of these coagulation markers shows 92.8% diagnostic accuracy 4, though this is secondary to APS testing.
What NOT to Test Routinely
MTHFR variants should NOT be tested. The 2025 ACMG technical standard explicitly states that MTHFR testing is not recommended for recurrent pregnancy loss, as recent meta-analyses show no significant association 5. This is supported by both ACOG and British hematology societies 5.
Factor V Leiden and Prothrombin G20210A testing should be reserved for specific circumstances (VTE at unusual sites, VTE provoked by pregnancy/postpartum, or positive family history of thrombophilia) 5, not as routine RSA screening.
Critical Pitfalls to Avoid
Do not order a "thrombophilia panel" reflexively - the 2025 guideline emphasizes that inherited thrombophilias have limited utility in most RSA cases 5
Timing matters for APS diagnosis - positive tests must be confirmed at least 12 weeks apart to meet diagnostic criteria 3
Distinguish physiologic pregnancy changes from pathology - normal pregnancy increases some coagulation factors; interpret results in context 3
Test during non-pregnant state when possible - pregnancy itself alters many immune and coagulation parameters 3
Algorithmic Approach
Step 1: Order APS panel + thyroid function tests for ALL patients with ≥2 pregnancy losses 1
Step 2: If APS panel positive → confirm with repeat testing ≥12 weeks later 3
Step 3: If thyroid antibodies elevated or TSH abnormal → treat and optimize before next conception 1
Step 4: If initial tests negative AND clinical suspicion for autoimmune disease → add ANA, complement levels 2
Step 5: If history suggests thrombotic tendency (not just pregnancy loss alone) → add protein S, protein C, antithrombin III 2, 4
The evidence strongly supports that early multi-indicator combined testing for patients with ≥2 miscarriages improves diagnostic accuracy and optimizes treatment plans 2. However, start with the highest-yield tests (APS and thyroid) rather than ordering everything simultaneously, as most cases will be identified with this focused approach.