{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,29]],"date-time":"2026-04-29T03:35:37Z","timestamp":1777433737339,"version":"3.51.4"},"reference-count":30,"publisher":"SAGE Publications","issue":"6","license":[{"start":{"date-parts":[[2002,11,1]],"date-time":"2002-11-01T00:00:00Z","timestamp":1036108800000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.sagepub.com\/page\/policies\/text-and-data-mining-license"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Ann Clin Biochem"],"published-print":{"date-parts":[[2002,11]]},"abstract":"<jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>Many maternal serum markers show concentration changes in Down's syndrome pregnancies but the magnitude of the change in median marker levels varies with gestation. To date these changes have not been accurately specified.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>\n                      The trends in marker median levels between 6 and 20 weeks of gestation were examined for alphafetoprotein (AFP), free \u03b2 human chorionic gonadotrophin (F \u03b2-hCG), total human chorionic gonadotrophin (ThCG) and pregnancy-associated plasma protein A (PAPP-A) by a meta-analysis of data obtained from our collaborative studies and routine screening programmes for Down's syndrome over a 10-year period. Data were available from between 709 and 1082 Down's syndrome pregnancies and from between 14 607 and 153 909 unaffected pregnancies for each marker. The median multiple of the median (MoM) and mean log\n                      <jats:sub>10<\/jats:sub>\n                      MoM for each marker at each completed week of gestation were estimated and the trend with gestation smoothed using a weighted least squares regression model.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      The gestational ages at which maximum separation of marker levels occurred, comparing affected and unaffected pregnancies, and the respective regressed median MoMs and mean log\n                      <jats:sub>10<\/jats:sub>\n                      MoMs, were: for AFP at 16 weeks, 0\u00b772 MoM, 0\u00b714288 log\n                      <jats:sub>10<\/jats:sub>\n                      MoM; for F \u03b2-hCG at 15 weeks, 2\u00b724 MoM, 0\u00b735034 log\n                      <jats:sub>10<\/jats:sub>\n                      MoM; for ThCG at 16 weeks, 1\u00b793 MoM, 0\u00b728548 log\n                      <jats:sub>10<\/jats:sub>\n                      MoM, as well as before 8 weeks (&lt; 0\u00b765 MoM, 0\u00b718853 log\n                      <jats:sub>10<\/jats:sub>\n                      MoM); and for PAPP-A before 8 weeks, &lt; 0\u00b733 MoM, 0\u00b747727 log\n                      <jats:sub>10<\/jats:sub>\n                      MoM.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>\n                      There is significant temporal variation in mean log\n                      <jats:sub>10<\/jats:sub>\n                      MoM values for the screening markers investigated. Screening algorithms, modified to take account of this variation, should allow more accurate gestation-specific risks to be calculated in individual pregnancies.\n                    <\/jats:p>\n                  <\/jats:sec>","DOI":"10.1177\/000456320203900604","type":"journal-article","created":{"date-parts":[[2014,2,5]],"date-time":"2014-02-05T16:51:35Z","timestamp":1391619095000},"page":"567-576","source":"Crossref","is-referenced-by-count":60,"title":["Temporal Changes in Maternal Serum Biochemical Markers of Trisomy 21 across the First and Second Trimester of Pregnancy"],"prefix":"10.1177","volume":"39","author":[{"given":"K","family":"Spencer","sequence":"first","affiliation":[{"name":"Endocrine Unit Clinical Biochemistry Department Harold Wood Hospital Gubbins Lane Romford Essex RM3 0BE, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"JA","family":"Crossley","sequence":"additional","affiliation":[{"name":"Duncan Guthrie Institute of Medical Genetics Yorkhill Glasgow G3 8SJ Scotland, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"DA","family":"Aitken","sequence":"additional","affiliation":[{"name":"Duncan Guthrie Institute of Medical Genetics Yorkhill Glasgow G3 8SJ Scotland, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"ABJ","family":"Nix","sequence":"additional","affiliation":[{"name":"Department of Medical Computing and Statistics University of Wales College of Medicine Heath Park Cardiff CF14 4XN Wales, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"FDJ","family":"Dunstan","sequence":"additional","affiliation":[{"name":"Department of Medical Computing and Statistics University of Wales College of Medicine Heath Park Cardiff CF14 4XN Wales, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"K","family":"Williams","sequence":"additional","affiliation":[{"name":"Department of Medical Computing and Statistics University of Wales College of Medicine Heath Park 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