Wednesday, May 8, 2024
5/8/2024
Interferometric near-infrared spectroscopy for transabdominal fetal oximetry The outcomes and cost of childbirth is an important issue that almost every family faced or will face. Compared to vaginal delivery, Cesarean section (C-section) has a higher cost, and may increase the health risk to both the baby and mother. About 32% of the deliveries are via C-section, which is much higher than the 10-15% ideal rate published by World Health Organization. A major triggering factor of C-section is a conservative prediction of fetal hypoxia during labor, which unfortunately has a high false-positive rate using the existing, widely-adopted intrapartum fetal monitoring technique of cardiotocography (CTG). Strikingly, since the introduction of CTG in the early 1970s, the rate of C-section deliveries in the US has risen five folds, while the rates of conditions associated with hypoxia remain unchanged. A noninvasive measurement of the fetal oxygen saturation during labor and delivery could provide obstetricians specific indicator of the necessity of emergency C-section. This may help to reduce the rate of unnecessary C-sections. Here, we propose a new transabdominal fetal oximetry (TFO) technique based on an innovative interferometric near-infrared spectroscopy (iNIRS) approach that could noninvasively measure the fetal arterial blood oxygen saturation. The iNIRS TFO measures the time-resolved reflectance of near-infrared light shining on the maternal abdomen. Our new method is distinctly different from the conventional pulse oximetry, and offers critical advantage to detect weak fetal signals buried in strong overwhelming maternal signal through the abdomen while greatly reducing the required light power on the tissue. Our approach distinguishes photons traversing different tissue depth, thus facilitating the separation of signal between the shallow maternal layer and the deep fetal layer. It greatly increases sensitivity to deep tissue signals and assures both an accurate and safe measurement. We conducted preliminary experiment on pregnant ewe and verified our technique could detect the fetal heartbeat through a single optical wavelength and a single detector, which presages the feasibility of iNIRS to measure fetal oxygen saturation. Here, we aim to build a two-wavelength iNIRS with a significantly improved measurement sensitivity to perform transabdominal fetal oximetry. The two optical wavelengths could extract the relative change of the oxygenated and deoxygenated hemoglobin during a cardiac cycle, and we will use time- division-multiplexing to switch between two optical wavelengths in the iNIRS setup. To improve the tissue penetration depth, we will increase the frequency tuning rate of the laser, use an innovative detection fiber and increase the number of detectors. All these approaches could increase the measurement sensitivity and thus the accessible tissue depth. Finally, we will develop advanced machine learning algorithms to extract the fetal oxygen saturation level from the raw measurements. We will perform the experiment in pregnant ewe model and validate the results with the arterial blood gas (ABG) test. The success of our project will make a significant impact on both the outcomes and cost of childbirth.
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