What is the normal progesterone level during the first trimester in nmol/L?

Normal Progesterone Levels in First Trimester Pregnancy

The normal serum progesterone level during the first trimester of pregnancy shows a linearly increasing trend from approximately 57.5 nmol/L at 5 weeks to 80.8 nmol/L at 13 weeks gestation, with a transient decline between weeks 6-8 during the luteal-placental shift. 1

Progesterone Patterns Throughout First Trimester

Progesterone is a critical hormone for implantation and maintenance of pregnancy. Its concentration follows a specific pattern during the first trimester:

• Early first trimester (5-6 weeks): Median levels start around 57.5 nmol/L 1
• Mid first trimester (6-8 weeks): A transient decline occurs during the luteal-placental shift, with lowest levels typically seen at week 7 2
• Late first trimester (9-13 weeks): Levels increase to approximately 80.8 nmol/L by 13 weeks 1

Clinical Significance of Progesterone Levels

Normal vs. Threatened Pregnancy

• Women with normal pregnancies have consistently higher progesterone levels than those with threatened miscarriage (approximately 10 nmol/L higher at every gestational week) 1
• Progesterone levels below 20.034 nmol/L (<6.3 ng/mL) are associated with a high likelihood of non-viable pregnancy (PPV 0.91-0.99) 3
• Levels above 63.6-79.5 nmol/L (≥20-25 ng/mL) are associated with viable pregnancies (NPV 0.89-0.99) 3

Factors Affecting Progesterone Levels

Several factors can influence serum progesterone levels during early pregnancy:

• Maternal age
• BMI
• Parity
• Gestational age 2

Important Caveats

• Single measurement limitations: A single low progesterone level (<5 ng/mL or <15.9 nmol/L) is suggestive but not diagnostic of a non-viable pregnancy 4
• Laboratory variations: Different assays may yield different results, and centers should refer to local laboratory guidelines 5
• Individualized interpretation: Normative values should be personalized to account for maternal factors and gestational age 2

Clinical Application

When evaluating progesterone levels in early pregnancy:

1. Consider the exact gestational age (expressed as weeks and days)
2. Account for maternal factors (age, BMI, parity)
3. Remember the transient decline during the luteal-placental shift (weeks 6-8)
4. Interpret results in context with other clinical findings and ultrasound results

While low progesterone is associated with pregnancy complications, a single low measurement should not be used in isolation to determine pregnancy viability, as some viable pregnancies may continue despite initially low progesterone levels 4.