Significantly decreased concentrations of MFAP4 (spontaneous PTD: median 6.9 ng/mL (IQR 4.2–8.1) vs term: median 8.5 ng/mL (IQR 5.6–19.2); p = 0.005), NGAL (spontaneous PTD: median 224.0 ng/mL (IQR 129.3–360.0) vs term: median 372.0 ng/mL (IQR (212.1–527.5); p = 0.011) and PAI-1 (spontaneous PTD: median 26.8 ng/mL (IQR (20.6–39.5) vs term: median 38.2 ng/mL (IQR 26.5–80.0); p = 0.010) in women with a spontaneous PTD were observed in the validation phase. The gene discussed is SERPINE1; the disease is Bjornstad syndrome.