(1191) Timing of Alpha-Feto Protein (AFP) Screening: Unveiling the Best Predictor for Adverse Pregnancy Outcomes

Objective: AFP at second trimester is used for prediction of neural tube defects and adverse pregnancy outcomes (APO). We hypothesized that first trimester is a better time for screening APOs than second trimester.

Study Design: This secondary analysis of a prospective cohort study included 2,245 patients. Pregnancies with known structural or chromosomal abnormalities, multifetal gestation, or incomplete data were excluded. Primary outcomes were preterm premature rupture of membranes (PPROM), preterm delivery (PD), and composite outcomes (CO: any occurrence of PPROM, PD, placental abruption, or preeclampsia). Alpha-fetoprotein (AFP) levels were measured in the first and second trimesters. A cutoff of 1.33 multiples of the median (MoM) for first trimester AFP, determined via receiver operating curve analysis, was used to predict adverse pregnancy outcomes (APOs) in the 1,713 first-trimester cases. The routine 2.5 MoM threshold was applied for second trimester AFP. A statistical model, adjusted for common risk factors (maternal age, sepsis, chronic hypertension, and preeclampsia), was used to assess associations with APOs, and the predictive values of first and second trimester AFP levels were compared in the statistical model.

Results: In the final analysis, 1,224 patients were included (Figure 1). Those with elevated first trimester AFP were more likely to be nulliparous (53.4% vs. 36.0%, p< 0.001) and have elevated second trimester AFP (5.54% vs. 0.65%, p< 0.001). Adjusted odds ratios for elevated first trimester AFP were 2.28 (p=0.004) for PPROM, 3.42 (p< 0.001) for PD, and 1.66 (p=0.009) for CO. A high negative predictive value (92.4-96.6%) was observed (Table 1). More patients with APOs were detected using first trimester AFP compared to second trimester AFP (p< 0.001 for all, Table 2).

Conclusion: First trimester AFP is a reliable biomarker with a high negative predictive value for excluding pregnancies at risk for APOs. In our study, it effectively replaced second trimester AFP, potentially eliminating the need for second trimester blood draws in care centers with advanced ultrasound capabilities.