Pregnancy-related complications affect approximately 15% of pregnancies and, if severe, can have long-term consequences. Timely recognition of physiological deterioration is known to reduce the prevalence and severity of complications. However pregnancy-associated changes in vital signs (blood pressure, heart rate, temperature, oxygen saturation, and respiratory rate) complicate the detection of abnormal physiology, and these changes are not well documented. This thesis describes the development of algorithms to ensure the collection of good-quality vital-sign data during the antenatal and postnatal stages of pregnancy, and the design of an evidence-based obstetric early warning score. Vital-sign information from 1,000 pregnant women during pregnancy, labour, and after delivery was collected during the 4P study using pulse oximetry, oscillometry for blood pressure measurement and a tympanic thermometer. Dynamic time warping was used to assess beat-by-beat quality in the photoplethysmograph (PPG) waveform obtained from the pulse oximeter. The resulting signal quality index enabled the exclusion of poor-quality sections and their associated measurements of heart rate and peripheral oxygen saturation. A robust measurement of respiratory rate was obtained by combining information from the PPG waveform, and accelerometer and gyroscope waveforms from a smartphone. After processing, frequency-based techniques, such as Fourier analysis and auto-regressive modelling, and time-domain peak detection were fused to estimate respiratory rate. When compared with the reference respiratory rate obtained from midwife measurement, the lowest mean absolute error of 1.16 breaths per minute was obtained from respiratory rate estimates from the y-axis of the gyroscope. Antenatal and postnatal reference ranges for each vital sign were developed with a standard polynomial multilevel (hierarchical) model using 10,000 vital sign measurements from 620 healthy women in the 4P study. Vital-sign trajectories confirmed known trends of blood pressure and heart rate changes during pregnancy, and provided new information about other vital-sign trends. Additional covariates were included to investigate the effect of parity and body mass index (BMI) on vital-sign trends. The outer centiles of the vital sign reference ranges were used to design an obstetric early warning score (C-ObsEWS) that took into account gestational age or time after delivery. The investigations in this thesis contribute additional knowledge of pregnancy-associated vital-sign changes, and lead to an initial proposal for an evidence-based obstetric early warning score specific to the stage of pregnancy.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:740810 |
| Date | January 2016 |
| Creators | Pullon, Rebecca |
| Contributors | Tarassenko, Lionel |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:c0992a87-29f1-40cc-8ff0-368cd1944bc9 |
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