The overall purpose of this study is to evaluate maternal-fetal tissue light scattering properties. The objectives of the study are: (i) integrate established mathematical principles of oxygen saturation to model with increasing accuracy the "body in a body" problem of fetus in mother; similar to existing pulse oximeters, the calculations will be integrated into software in the final commercial product; (ii) obtain human measurements against which both computational models and animal data can be compared.

This is a prospective, observational, non-significant risk study. The study involves using non-invasive devices that measure fetal depth and tissue light scattering on the maternal abdomen. Ultrasound assessment will be performed, and multiple images taken at various locations on the abdomen. All images will be captured with minimal probe pressure applied to allow accurate ascertainment of depth. Images will be anonymized, and all study data will be coded with a unique identifier. Key maternal descriptive statistics will be recorded from the medical record including BMI, height, weight (kg), parity, age and gestational age.

The ISS device is a customized commercial frequency domain oximeter (Imagent, ISS Inc.; http://www.iss.com/biomedical/instruments/imagent.html) with multiple laser sources and multiple detectors. This instrument is safe, uses non-ionizing radiation.

The Raydiant Lumerah device is a non-invasive fetal pulse oximeter that measures fetal arterial oxygen saturation using safe, non-invasive, transabdominal near-infrared spectroscopy. The Lumerah device will be positioned on the maternal abdomen of women volunteers in the late 3rd trimester.

Inclusion Criteria:

1. Women with singleton, healthy pregnancy at gestational age ≥ 36 weeks
2. Age > 18 years
3. Willing to come in for testing outside of routine business hours (including Saturdays)

Exclusion Criteria:

1. Age <18
2. Multiple gestation (twins, triplets)
3. Presentation other than vertex or breech
4. < 36 weeks of gestation

Pregnant women

The data are specific to this device only.