First-trimester reference ranges for decidual thickness and its relation to progesterone levels

The present study aimed to provide normal reference ranges for decidual thickness measured ultrasonographically in healthy first-trimester pregnancies and to evaluate whether there was a relationship between decidual thickness and serum progesterone levels.

Decidual thickness of 173 women with a healthy gestation between 6+0 and 9+6 weeks was measured ultrasonographically and serum progesterone concentration was determined. Distribution of decidual thickness at each gestational week and its relation with serum progesterone levels was evaluated.

Mean decidual thickness was 6.8, 5.7, 5.5, and 6.1 mm at 6th, 7th, 8th, and 9th gestational weeks, respectively. Decidual thickness showed a mild negative correlation with gestational week (ρ=-0.207, P=0.006) and a mild positive correlation with serum progesterone concentrations (ρ=0.191, P=0.021).

The present study provided normal reference ranges for decidual thickness in healthy pregnancies in the first trimester. The association found between decidual thickness and progesterone levels might shed light on further studies investigating the predictive factors of pregnancy loss and might lead to changes in the management of threatened miscarriage.