What are normal serum progesterone levels during pregnancy?

Normal Serum Progesterone Levels During Pregnancy

Serum progesterone levels increase linearly during early pregnancy, with normal median values ranging from approximately 57.5 nmol/L (18 ng/mL) at 5 weeks to 80.8 nmol/L (25 ng/mL) at 13 weeks gestation in normal pregnancies. 1

First Trimester Progesterone Levels

• Progesterone is a critical hormone in early pregnancy that increases linearly with gestational age from 5 to 13 weeks 1
• In normal pregnancies, median serum progesterone concentration demonstrates a linearly increasing trend from 57.5 nmol/L to 80.8 nmol/L from 5 to 13 weeks gestation 1
• Progesterone levels below 6.3 ng/mL (20 nmol/L) are associated with a high likelihood of non-viable pregnancy (sensitivity 73.1%, specificity 99.2%) 2
• Progesterone levels above 20-25 ng/mL (63.6-79.5 nmol/L) are associated with a high likelihood of viable pregnancy (sensitivity 91.3%, specificity 75%) 2

Physiological Role of Progesterone in Pregnancy

• Progesterone is produced by the corpus luteum until completion of the luteal-placental shift at approximately 6-10 weeks following last menstruation 3
• Progesterone functions as an endogenous vasodilator that contributes to decreased systemic vascular resistance during pregnancy 4
• Increased ventilation (20-40% above baseline by term) is mediated by elevated serum progesterone levels, producing a mild respiratory alkalosis 4
• This respiratory change results in arterial carbon dioxide pressure of approximately 28-32 mm Hg and plasma bicarbonate level of 18-21 mEq/L 4

Clinical Significance of Progesterone Levels

• Low progesterone levels are associated with threatened miscarriage, with levels approximately 10 nmol/L lower at every gestational week compared to normal pregnancies 1
• Women who eventually miscarry show only a marginal and non-significant increase in serum progesterone from 19.0 to 30.3 nmol/L from 5 to 13 weeks gestation 1
• A single progesterone level provides clinically useful prognostic information on pregnancy viability 2
• However, a single serum progesterone level <5 ng/mL is suggestive, but not diagnostic, of a nonviable pregnancy 3

Progesterone in Twin Pregnancies

• In spontaneous dichorionic-diamniotic twin gestations, progesterone levels of 58 nmol/L at 7 weeks and 51 ng/ml at 10 weeks have predictive value for viable intrauterine twin pregnancies 5

Clinical Applications and Monitoring

• Serial serum progesterone measurements can be used to evaluate corpus luteum function during early gestation 6
• Luteal phase serum progesterone levels between 2-10 ng/ml and levels below 15 ng/ml in the first 10 weeks of gestation may indicate corpus luteum dysfunction 6
• Management of patients with corpus luteum dysfunction can be monitored with serial serum progesterone measurements 6

Important Caveats

• A single low progesterone value should not be used as an absolute cutoff for determining pregnancy viability, as viable pregnancies have been reported with very low initial progesterone levels 3
• Routine uterine curettage during evaluation of pregnancy of unknown location using a single low progesterone level as an absolute cutoff may result in interruption of a desired, viable pregnancy 3
• When interpreting progesterone levels, consider the specific laboratory assay used, as reference ranges may vary between laboratories 2