From the Guidelines
C-reactive protein (CRP) levels typically increase during normal pregnancy, with values often rising above the non-pregnant reference range, and can be measured as part of pregnancy registries in rheumatology, as recommended by the EULAR guidelines 1.
CRP Levels During Pregnancy
- CRP levels may double from baseline during the first trimester, and by the third trimester, they can increase up to 5-fold, reaching values of 3-10 mg/L in uncomplicated pregnancies.
- This physiological elevation occurs due to the inflammatory state associated with normal pregnancy as the maternal immune system adapts to accommodate the developing fetus.
- Despite this normal increase, CRP remains a useful marker for detecting infections or inflammatory conditions during pregnancy, though interpretation requires consideration of these pregnancy-induced elevations.
Clinical Considerations
- Significantly elevated CRP levels (typically >10 mg/L) may indicate infection, preeclampsia, or other pregnancy complications requiring further investigation.
- Healthcare providers should use pregnancy-specific reference ranges when interpreting CRP values and consider the clinical context, gestational age, and other laboratory and clinical findings when evaluating pregnant patients with elevated CRP levels.
- Regular monitoring may be necessary in high-risk pregnancies or when infection or inflammation is suspected, as part of a comprehensive approach to pregnancy care, including the assessment of other relevant factors, such as disease activity and patient-reported outcomes 1.
From the Research
C-Reactive Protein Levels During Pregnancy
- C-Reactive Protein (CRP) levels during pregnancy have been studied to understand their role in diagnosing infections and predicting complications 2, 3, 4, 5, 6.
- Median CRP values for women not in labor ranged from 0.7-0.9 mg/dL, depending on gestational age, with 95% of the values being 1.5 mg/dL or lower 2.
- CRP values are higher in pregnant women than in non-pregnant individuals, with an upper reference limit of 19 mg/L in each trimester 3.
- CRP levels increase linearly with body mass index (BMI) 3.
- Elevated CRP levels during the first trimester of pregnancy may be indicative of preeclampsia and intrauterine growth restriction 5.
- A cutoff value of >1.86 μg/mL for CRP has been found to be predictive of maternal adverse outcomes (MAO) 4.
- CRP levels do not cross the placental barrier and may be useful in diagnosing infections in newborns 6.
Trimester-Specific Reference Intervals
- Trimester-specific reference intervals for CRP have been defined, with an upper reference limit of 19 mg/L in each trimester 3.
- Using pregnancy-specific reference intervals for CRP can improve diagnostic accuracy for infection 3.
- CRP levels are similar in each trimester, with no consistent change in CRP levels with gestational age among serially sampled women not in labor 2.
Predictive Value of CRP
- Elevated CRP levels at midpregnancy can predict gestational complications, including maternal and neonatal adverse outcomes 4.
- CRP levels >1.86 μg/mL have been found to predict MAO, considering maternal age, hypertension, and gestational diabetes mellitus (GDM) 4.
- Mean CRP levels were significantly elevated in women who later developed preeclampsia or delivered a growth-restricted baby 5.