What is the normal D-dimer range at 22 weeks gestation?

D-Dimer Normal Range at 22 Weeks Gestation

At 22 weeks gestation (mid-second trimester), the normal D-dimer range is approximately 0.14-0.75 mg/L (140-750 μg/L), though values up to 3.26 mg/L may still be within normal limits depending on the assay used. 1, 2

Trimester-Specific Reference Ranges

D-dimer levels increase progressively throughout normal pregnancy, making standard non-pregnant cutoffs (0.5 mg/L) inappropriate for pregnant women 3, 4:

Published Reference Intervals by Trimester:

First Trimester (5-11 weeks):

• 0.11-0.40 mg/L 1
• 0.169-1.202 mg/L (alternative assay) 2

Second Trimester (13-20 weeks):

• 0.14-0.75 mg/L 1
• 0.393-3.258 mg/L (alternative assay) 2

Third Trimester (25-35 weeks):

• 0.16-1.3 mg/L 1
• 0.551-3.333 mg/L (alternative assay) 2

Critical Clinical Context for 22 Weeks

At 22 weeks gestation, approximately 4.8% of healthy pregnant women will have D-dimer levels exceeding the standard non-pregnant cutoff of 0.50 mg/L 1. This percentage increases dramatically as pregnancy progresses—by the third trimester, 98-100% of healthy pregnant women have D-dimer levels above 0.50 mg/L 5, 6.

Why Standard Cutoffs Fail in Pregnancy:

• The physiologic increase in D-dimer reflects normal pregnancy-related hypercoagulability, not pathologic thrombosis 3, 4
• Using non-pregnant reference ranges leads to excessive false-positive results and unnecessary imaging 4, 5
• D-dimer testing has extremely limited utility for excluding VTE in pregnancy, particularly after the first trimester 3, 4

Clinical Algorithm for Suspected VTE at 22 Weeks

The American Thoracic Society/Society of Thoracic Radiology explicitly recommends AGAINST using D-dimer to exclude pulmonary embolism in pregnancy 4. Instead:

For Suspected DVT:

1. Proceed directly to bilateral compression ultrasound of lower extremities as first-line test 3, 4
2. If ultrasound confirms DVT, initiate therapeutic LMWH immediately 4
3. Do not rely on D-dimer results to guide decision-making 4

For Suspected PE:

1. Proceed directly to chest imaging (perfusion scan or CT pulmonary angiography) if clinical suspicion exists 4
2. Do not withhold imaging based on D-dimer results alone 4
3. Perfusion lung scintigraphy delivers only 10-350 μGy to the fetus, well below the 50,000 μGy safety threshold 3

Important Assay-Specific Considerations

D-dimer reference ranges are NOT transferable between different laboratory assays or institutions 7. The wide variation in published reference ranges (0.14-0.75 mg/L versus 0.393-3.258 mg/L for second trimester) reflects different assay methodologies 2, 1:

• Latex-based immunoturbidimetric assays 2
• MDA turbidimetric assays 5
• Different reporting units (FEU versus DDU, with FEU approximately 2-fold higher) 7

Always verify the specific reference range for your laboratory's assay method 7.

When Markedly Elevated D-Dimer Indicates Pathology

D-dimer levels several-fold above the upper range of normal for pregnancy (>2 mg/L) should raise concern for pathologic coagulopathy rather than physiologic pregnancy changes 4. At 22 weeks, this would mean levels substantially exceeding 3.26 mg/L 2.

Pathologic causes to consider:

• Venous thromboembolism (DVT/PE) 4
• Disseminated intravascular coagulation (DIC) 4
• Placental abruption (if accompanied by vaginal bleeding)
• Assess platelet count, fibrinogen, and fibrin degradation products if DIC suspected 4

Key Clinical Pitfalls to Avoid

• Never use the standard non-pregnant cutoff of 0.5 mg/L to exclude VTE after the first trimester 4, 5
• Never withhold imaging in symptomatic pregnant patients based on D-dimer alone 4
• Do not interpret isolated breathlessness as PE without additional acute symptoms—breathlessness is common in normal pregnancy 3
• Always draw arterial blood gases in the upright position, as PaO2 may be up to 2 kPa lower in the supine position during third trimester 3