Normal Progesterone Levels in Early Pregnancy
In normal early pregnancy, serum progesterone levels range from approximately 57.5 nmol/L (18.3 ng/mL) at 5 weeks to 80.8 nmol/L (25.7 ng/mL) at 13 weeks gestation, demonstrating a linear increase throughout the first trimester. 1
Gestational Age-Specific Reference Ranges
Normal pregnancy progesterone trajectory:
- Median progesterone increases linearly from 57.5 nmol/L at 5 weeks to 80.8 nmol/L at 13 weeks gestation in uncomplicated pregnancies 1
- This represents an approximate increase of 2-3 nmol/L per week during the first trimester 1
Critical diagnostic thresholds for pregnancy viability:
- Progesterone ≥20-25 ng/mL (63.6-79.5 nmol/L): 91.3% sensitivity for viable pregnancy, with 89-99% negative predictive value depending on clinical context 2
- Progesterone <6.3 ng/mL (<20.034 nmol/L): 73.1% sensitivity and 99.2% specificity for non-viable pregnancy, with 91-99% positive predictive value for pregnancy loss 2
- Progesterone <10 ng/mL: 66.5% sensitivity and 96.3% specificity for non-viable pregnancy in symptomatic women 3
Clinical Context and Interpretation
Symptomatic vs asymptomatic pregnancies:
- Women with threatened miscarriage have median progesterone levels approximately 10 nmol/L lower at every gestational week compared to normal pregnancies 1
- In threatened miscarriage, median progesterone ranges from 41.7 nmol/L at 5 weeks to 78.1 nmol/L at 13 weeks 1
Progesterone patterns predicting pregnancy outcome:
- Women who ultimately miscarry show only marginal, non-significant increases in progesterone (19.0 to 30.3 nmol/L from 5-13 weeks) 1
- This contrasts sharply with the robust linear increase seen in viable pregnancies 1
Important Clinical Caveats
Limitations of single progesterone measurements:
- While progesterone <5 ng/mL is highly suggestive of non-viable pregnancy, rare cases of viable pregnancy have been documented with levels as low as 1.2 ng/mL 4
- A single progesterone value should not be used as the sole criterion for pregnancy termination, as this may result in interruption of a desired viable pregnancy 4
- Progesterone cannot reliably differentiate ectopic pregnancy from miscarriage, as mean values overlap significantly (5.9 ng/mL for ectopic vs 6.8 ng/mL for miscarriage, p=0.067) 5
Optimal diagnostic approach:
- For women with symptoms and inconclusive ultrasound, progesterone 3.2-6 ng/mL predicts non-viable pregnancy with 74.6% sensitivity and 98.4% specificity, raising probability from 73.2% to 99.2% 3
- Serial measurements combined with ultrasound and β-hCG trends provide superior diagnostic accuracy compared to single progesterone values 6
- The luteal-placental shift occurs at 6-10 weeks gestation, after which progesterone production transitions from corpus luteum to placenta 4