Correlation between spontaneous preterm birth and mid-trimester maternal serum estriol.

Objective: Elevated third trimester salivary estriol levels have been associated with preterm birth. We evaluated whether maternal estriol concentrations from second trimester serum correlated with preterm delivery.

Methods: A retrospective cohort study of 7767 patients evaluated with second trimester aneuploidy screening. Unconjugated serum estriol was measured by immunoassay, expressed as multiples of the median (MoM) for gestational age and evaluated for association with preterm (<37 week) birth.

Results: Elevated maternal serum estriol was significantly associated with preterm birth (1.15 MoM versus 1.03 MoM for delivery at term, OR 1.69 CI 1.41 to 2.02). 9.95% of spontaneously laboring patients <34 weeks had estriol MoM > 2, as opposed to 6.23% of >34 week deliveries (p = 0.031). There was a direct correlation between level of estriol concentrations and gestational age at time of delivery.

Conclusions: Elevated second trimester maternal serum unconjugated estriol is independently associated with a higher rate of spontaneous preterm birth.