Preterm infants are highly vulnerable and may suffer from multiple life-threatening conditions that manifest low tissue oxygenation (StO2). Near infrared spectroscopy (NIRS) is a technique available to non-invasively and safely monitor the tissue oxygenation status (StO2), which can be beneficial or live saving for this fragile patient population. Unfortunately, traditional NIRS devices show a broad variability when applied to the abdomen (Bailey & Mally 2016). The novel device is designed especially for application of NIRS on the abdomen of preterm infants.

Each child will be measured over a time span of three days with the novel NIRS device.

1. A two-hour measurement is performed in measurement phase 1
2. Additionally, the sensor will be placed five times onto the abdomen for 1-minute measurements, which constitutes measurement phase 2.
3. The final measurement phase 3 lasts for up to 70 hours.

A total of two ultrasound (US) examination on the abdomen are performed during the first two measurement phases to assess the presence of air and stool in the abdomen.

Additional assessment of SpO2 is performed throughout. Aside from the US and SpO2 measurement, no additional procedures will be performed.

The NIRS measurement will not disturb necessary clinical and nursing procedures.

Inclusion Criteria:

1. Preterm infants with Gestational age less than 35 0/7 weeks
2. Signed Informed consent of the legal representative(s) is received after being informed. The consent form is signed by one legal representative, which is likely to be either the mother or the father. Only married fathers or those listed on the birth certificate are considered under UK regulations. In the case of non-married father, the mother must provide consent.
3. Clinically stable condition. The clinical stability is to be reconfirmed before the start and checked during the measurement.

Exclusion Criteria:

1. Injured, hypersensitive or bruised skin present on the abdomen,
2. Existence of clinical instability at any time during the investigation leads to exclusion, if ordered so by the physician entrusted with the investigation,
3. Any medical care equipment, e.g. patches, dressing, umbilical arterial or venous catheter, blood supply, etc., prohibiting correct placement of the sensors,
4. Severe Congenital malformations,
5. Clinical abdominal concerns
6. Severe metabolic disorders,
7. Early onset sepsis,
8. Inability of legal representatives to understand the purpose of the clinical trial due to language barriers such as the insufficient ability to understand the spoken or written language,
9. The treatment of newborn jaundice with light during measurement time phase 1 and 2,
10. Previous enrolment into the current study,
11. Family members, employees and other dependent persons of the investigator,
12. Participation in another study with investigational drug/device within the preceding days and during the present study which may influence abdominal oxygen saturation.
13. Known silicone allergy