Introduction
This study aims to investigate the role of CEACAM1 in preterm birth. Preterm birth is a phenomenon with numerous triggers, with the immune system hypothesized to play a significant role in the process, aligning with the concept of ’birth as an immunological rejection phenomenon’. There are several approaches to predict preterm birth, and the determination of sCEACAM1 levels, a member of the carcinoembryonic antigen family, may serve as a potential candidate biomarker.

Methods
A single-center prospective case series study included 67 pregnant women aged 18 years or older who presented before 37 weeks of gestation with signs of preterm birth in the years 2021–2023. At the time of admission, CEACAM1 was determined in maternal blood.

Results
The median sCEACAM1 levels were significantly higher in women who delivered preterm compared to those who delivered at term respectively, 5014 pg/ml (IQR: 3592–8826) vs. 3353 pg/ml (IQR: 2354–5049) (p = 0.016).
The median sCEACAM1 level in the group with PPROM (premature preterm rupture of membranes) at 34 weeks’ gestation was 7001 pg/ml (IQR: 5683–13509), while the median sCEACAM1 level in the group without PPROM at 34 weeks’ gestation was 3884 pg/ml (IQR; 2461–4985) (p < 0.001).

Conclusions
Pregnant women with preterm birth and/or PPROM before 34 weeks’ gestation have higher CEACAM1 levels compared to women with threatened preterm labor who finally had labot at term. The results suggest early activated immune system as a potential pathomechanism of preterm delivery.