Iles, Ray K, et al. “The Importance of Gestational Age in First Trimester, Maternal Urine MALDI-Tof MS Screening Tests for Down Syndrome”. Annals of Proteomics and Bioinformatics, vol. 3, no. 1, Dec. 2019, pp. 010-7, doi:10.29328/journal.apb.1001008.