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, with a linear increase throughout the first trimester. 1
Gestational Age-Specific Reference Ranges
Normal pregnancy progesterone distribution:
- 5 weeks gestation: Median 57.5 nmol/L (18.3 ng/mL) 1
- 13 weeks gestation: Median 80.8 nmol/L (25.7 ng/mL) 1
- Linear increase pattern: Progesterone demonstrates a consistent upward trend throughout weeks 5-13 of gestation 1
The 10th to 90th percentile range widens as pregnancy advances, reflecting normal physiologic variation 1.
Clinical Thresholds for Viability Assessment
When evaluating symptomatic patients with bleeding or pain:
Progesterone <6.3 ng/mL (<20 nmol/L): Indicates non-viable pregnancy with 99.2% specificity and 73.1% sensitivity, yielding a positive predictive value of 91-99% depending on prevalence 2, 3
Progesterone 20-25 ng/mL (63.6-79.5 nmol/L): Indicates viable pregnancy with 75% specificity and 91.3% sensitivity, yielding a negative predictive value of 89-99% for non-viability 2
Progesterone 10 ng/mL (31.8 nmol/L): When used as a threshold in symptomatic women, predicts non-viable pregnancy with 96.3% specificity and 66.5% sensitivity 3
Critical caveat: A single progesterone level <5 ng/mL is suggestive but not absolutely diagnostic of non-viable pregnancy, as rare cases of viable pregnancies have been documented with levels as low as 1.2 ng/mL 4. Routine uterine curettage based solely on this threshold may interrupt desired viable pregnancies 4.
Comparison: Normal vs. Threatened Miscarriage
Threatened miscarriage progesterone patterns:
- Median levels are uniformly lower by approximately 10 nmol/L at every gestational week compared to normal pregnancies 1
- At 5 weeks: Median 41.7 nmol/L (13.3 ng/mL) in threatened miscarriage vs. 57.5 nmol/L in normal pregnancy 1
- At 13 weeks: Median 78.1 nmol/L (24.8 ng/mL) in threatened miscarriage vs. 80.8 nmol/L in normal pregnancy 1
Pregnancies ending in miscarriage: Show marginal, non-significant increase from 19.0 to 30.3 nmol/L (6.0 to 9.6 ng/mL) between 5-13 weeks, contrasting sharply with the robust linear increase seen in viable pregnancies 1.
Physiologic Context
Corpus luteum function: Progesterone is produced by the corpus luteum until completion of the luteal-placental shift at approximately 6-10 weeks following last menstruation 4. During early gestation (first 10 weeks), serum progesterone levels below 15 ng/mL (47.7 nmol/L) are considered diagnostic of corpus luteum dysfunction 5.
Clinical Application Algorithm
For asymptomatic women with confirmed intrauterine pregnancy:
- Routine progesterone testing is not indicated 6
- Progesterone levels naturally increase linearly from 5-13 weeks 1
For symptomatic women (bleeding/pain) with inconclusive ultrasound:
- Progesterone <6.3 ng/mL: 99.2% probability of non-viable pregnancy 2, 3
- Progesterone 6.3-20 ng/mL: Indeterminate zone requiring serial hCG and repeat ultrasound 2, 3
- Progesterone ≥20-25 ng/mL: >90% probability of viable pregnancy 2
Important limitation: Single progesterone measurements should not be used in isolation for clinical decision-making, particularly regarding pregnancy termination, as rare exceptions exist where very low levels (<5 ng/mL) can still be associated with viable pregnancies 4.