{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T11:22:01Z","timestamp":1785410521412,"version":"3.56.0"},"reference-count":26,"publisher":"MDPI AG","issue":"13","license":[{"start":{"date-parts":[[2026,7,1]],"date-time":"2026-07-01T00:00:00Z","timestamp":1782864000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100002241","name":"Japan Science and Technology Agency","doi-asserted-by":"publisher","award":["JPMJPF2108"],"award-info":[{"award-number":["JPMJPF2108"]}],"id":[{"id":"10.13039\/501100002241","id-type":"DOI","asserted-by":"publisher"}]},{"award":["JPMJPF2108"],"award-info":[{"award-number":["JPMJPF2108"]}],"id":[{"id":"https:\/\/ror.org\/00097mb19","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>This study proposes a multivariate analytical framework for transabdominally recorded intrauterine acoustic signals (TRIAS) and evaluates spectral changes across gestation. Using a digital stethoscope, 60 recordings were obtained from 44 pregnant women (\u226514 weeks). Power spectral density (PSD) was calculated (30\u20132000 Hz) and analyzed using ordinary least squares (OLS) regression, principal component analysis (PCA), and partial least squares regression (PLSR). A consistent spectral peak was observed at 300\u2013400 Hz. OLS revealed a significant decrease in PSD levels within 400\u2013600 Hz (specifically 478.5 Hz and 521.5 Hz) during the second trimester (t \u2248 \u22123.5), while changes were minimal in the third trimester. PCA identified maternal heart rate as the primary contributor to the first principal component, and PLSR showed that maternal cardiovascular dynamics and gestational progression were associated with distinct, largely independent components in the multivariate space. These results suggest that TRIAS may capture a composite maternal\u2013fetal acoustic environment influenced by both maternal circulation and gestational uterine alterations. Specifically, the observed second-trimester spectral changes may reflect fluid dynamic or structural transitions\u2014such as variations in amniotic fluid volume\u2014and may serve as a baseline for future monitoring research.<\/jats:p>","DOI":"10.3390\/s26134150","type":"journal-article","created":{"date-parts":[[2026,7,1]],"date-time":"2026-07-01T10:41:01Z","timestamp":1782902461000},"page":"4150","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Multivariate Spectral Analysis of Transabdominally Recorded Intrauterine Acoustic Signals (TRIAS) Across Gestation"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0009-0004-8441-9884","authenticated-orcid":false,"given":"Ryo","family":"Tamaki","sequence":"first","affiliation":[{"name":"Department of Obstetrics, Hokkaido University Hospital, Kita\u2013ku N15 W7, Sapporo 060-8638, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Fuyuka","family":"Igarashi","sequence":"additional","affiliation":[{"name":"Department of Obstetrics, Hokkaido University Hospital, Kita\u2013ku N15 W7, Sapporo 060-8638, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0001-8408-3370","authenticated-orcid":false,"given":"Ryutaro","family":"Yamamoto","sequence":"additional","affiliation":[{"name":"Department of Obstetrics, Hokkaido University Hospital, Kita\u2013ku N15 W7, Sapporo 060-8638, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1033-3920","authenticated-orcid":false,"given":"Hiroshi","family":"Asano","sequence":"additional","affiliation":[{"name":"Department of Obstetrics, Hokkaido University Hospital, Kita\u2013ku N15 W7, Sapporo 060-8638, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Akira","family":"Oku","sequence":"additional","affiliation":[{"name":"Department of Obstetrics, Hokkaido University Hospital, Kita\u2013ku N15 W7, Sapporo 060-8638, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Keiichiroh","family":"Akabane","sequence":"additional","affiliation":[{"name":"Department of Obstetrics, Hokkaido University Hospital, Kita\u2013ku N15 W7, Sapporo 060-8638, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kiwamu","family":"Noshiro","sequence":"additional","affiliation":[{"name":"Department of Obstetrics, Hokkaido University Hospital, Kita\u2013ku N15 W7, Sapporo 060-8638, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ami","family":"Hosokawa","sequence":"additional","affiliation":[{"name":"Department of Obstetrics, Hokkaido University Hospital, Kita\u2013ku N15 W7, Sapporo 060-8638, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1424-4044","authenticated-orcid":false,"given":"Yoshihiro","family":"Saito","sequence":"additional","affiliation":[{"name":"Department of Obstetrics, Hokkaido University Hospital, Kita\u2013ku N15 W7, Sapporo 060-8638, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hidemichi","family":"Watari","sequence":"additional","affiliation":[{"name":"Department of Obstetrics, Hokkaido University Hospital, Kita\u2013ku N15 W7, Sapporo 060-8638, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9236-9945","authenticated-orcid":false,"given":"Takeshi","family":"Umazume","sequence":"additional","affiliation":[{"name":"Department of Obstetrics, Hokkaido University Hospital, Kita\u2013ku N15 W7, Sapporo 060-8638, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,1]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"745","DOI":"10.7863\/ultra.33.5.745","article-title":"Fetal imaging: Executive summary of a joint NICHD, AIUM, ACOG, ACR, SMFM, SRU workshop","volume":"33","author":"Reddy","year":"2014","journal-title":"J. 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