Due to copyright issues, an electronic copy of the thesis must be ordered from the faculty. For the faculty to have time to process the order, the order must be received by the faculty at the latest 2 days before the public defence. Orders received later than 2 days before the defence will not be processed. After the public defence, please address any inquiries regarding the thesis to the candidate.
Trial Lecture – time and place
See Trial Lecture.
Adjudication committee
- First opponent: Associate Professor Anne Nødgaard Weidemann Sørensen, North Denmark Regional Hospital,
- Second opponent: Associate professor Ragnar Kvie Sande, Stavanger Universitetssykehus,
- Third member and chair of the evaluation committee: Associate professor Lil-Sofie Ording Müller, University of Oslo
Chair of the Defence
Professor Hilde Lurås, University of Oslo
Principal Supervisor
Marit Camilla Haavaldsen, Akershus University Hospital
Summary
The placenta is essential for fetal growth and normal pregnancy development. Abnormal placental size at birth has been associated with adverse outcomes such as stillbirth and cerebral palsy.
Most knowledge of placental size and its association with pregnancy outcomes is based on studies of delivered placentas. Improved understanding of placental growth and size in ongoing pregnancies requires easily available imaging methods for assessing placental size in utero.
The overarching aim of this thesis was to evaluate whether ultrasound can provide reliable and valid measurements of placental size. Ultrasound is the preferred imaging modality in antenatal care due to its wide availability and routine clinical use. We used data from the Placental Volume Study (PLAVO), in which pregnant women and their placentas were examined using 2D and 3D ultrasound, with magnetic resonance imaging (MRI) used as the reference standard.
Placental size measurements using 2D and 3D ultrasound showed poor to moderate correlation with MRI, and placental volume measured using 3D ultrasound systematically underestimated placental size. These findings are likely related to the large size, variable shape, and location of the placenta in utero, which make complete visualization difficult due to acoustic shadowing and a limited field of view.
To address these challenges, we developed and tested a new ultrasound method using 2D ultrasound with position tracking, enabling reconstruction of the placenta from multiple images. Automatic image segmentation was performed using a convolutional neural network trained to identify the placenta in the images. Free movement of the 2D ultrasound probe enabled visualization of the placenta from multiple angles, allowing more placental tissue to be included in the ultrasound acquisitions compared with 3D ultrasound.
This thesis demonstrates that ultrasound measurements of placental size are challenging. Hopefully, this work may contribute to improved ultrasound methods for measuring placental size.
Additional information
Contact the research support staff.