What are normal progesterone levels in the first trimester?

Normal Progesterone Levels in the First Trimester

Normal progesterone levels in the first trimester show an increasing trend with a transient decline between gestational weeks 6-8, corresponding to the luteal-placental shift, with lowest levels typically seen at week 7. 1

Progesterone Pattern During First Trimester

• Progesterone is a critical steroid hormone produced initially by the corpus luteum and later by the placenta 1
• Progesterone functions as an endogenous vasodilator that contributes to decreased systemic vascular resistance during pregnancy 2
• Serum progesterone shows an increasing trend throughout the first trimester, with a characteristic dip between weeks 6-8 during the luteal-placental shift 1
• The lowest progesterone levels are typically observed around week 7 of gestation 1

Normal Progesterone Range Values

• While specific normal ranges vary by laboratory, studies suggest the following patterns:
  • Progesterone levels ≥20-25 ng/mL (63.6-79.5 nmol/L) are associated with viable pregnancies in over 90% of cases 3
  • Levels <6.3 ng/mL (<20.034 nmol/L) are associated with non-viable pregnancies in more than 90% of cases 3
  • The intermediate range (6.3-19.9 ng/mL) has less predictive value for pregnancy viability 3

Factors Affecting Progesterone Levels

• Several factors can influence progesterone levels during the first trimester:
  • Maternal age 1
  • Body mass index (BMI) 1
  • Parity 1
  • Gestational age 1
  • Pregnancy outcome 1

Clinical Implications

• Low progesterone levels are associated with higher miscarriage risk, but a single low value should not be used as the sole determinant of pregnancy viability 4
• A case report documented a viable pregnancy that progressed despite a very low first trimester progesterone level of 1.2 ng/mL 4
• When evaluating first trimester vaginal bleeding, progesterone levels alone cannot reliably differentiate between ectopic pregnancy and miscarriage 5

Important Caveats

• A single serum progesterone measurement should not be used in isolation to make clinical decisions about pregnancy viability 4, 3
• Local laboratory reference ranges should be consulted as values may vary between institutions 6
• The first trimester is defined as gestational age ≤13 weeks 6 days 6
• Combined markers (estradiol and progesterone) at 7-9 weeks may provide better predictive value for pregnancy outcomes than progesterone alone 7