The hemolytic disease of newborns (HDN) is one of the most significant risk factors for hyperbilirubinemia. Studies have shown that end-tidal carbon monoxide-corrected (ETCOc) correlated with the rate of bilirubin production in the body and thus can be a good surrogate to quantify hemolysis and identifying the high-risk infants. However, there is insufficient clinical evidence regarding the early prediction of hemolytic hyperbilirubinemia using ETCOc. This study hypothesizes that early postnatal ETCOc levels are significantly associated with the risk of hemolytic hyperbilirubinemia requiring treatments within 14 days after birth, and early postnatal ETCOc can be a good indicator for early prediction of hemolysis. In addition, the investigators aim to investigate the relationship between the characteristics of treatments for hyperbilirubinemia and ETCOc.

Study design: this study is a multi-center, prospective observational cohort study on neonatal jaundice. Eligible participants will be enrolled in the well-baby nursery and neonatal intensive care units (NICU). Transcutaneous bilirubin and/or total serum bilirubin (TCB/TSB) will be measured as per clinical practice and simultaneous ETCOc (within time intervals ≤3 hours) will be monitored until (1) the newborn is discharged with the mother, or (2) until 72 hours after birth or (3) requiring the treatments for hyperbilirubinemia (phototherapy and/or exchange transfusion) (whichever comes first). For infants who do not require treatments for hyperbilirubinemia (phototherapy and/or exchange transfusion) during the stay in well-baby nursery or in the NICU within 72 hours after birth, they will be followed up via telephone or outpatient clinic visits during the first 14 days of life (DOL).

The primary outcome is the first occurrence of hemolytic hyperbilirubinemia requiring treatments within DOL14. For participants who have the primary outcome occurred within DOL14, follow-up calls/visits will continue until DOL28 to record the readmissions due to hyperbilirubinemia within 28 DOL . The secondary outcomes are 1) the incidence of hemolytic diseases of newborns; 2) characteristics of treatment for hemolytic hyperbilirubinemia: postnatal age when requiring the treatment, levels of TCB/TSB/ETCOc during hospitalization, length of stay, length of phototherapy, courses of phototherapy, exchange of transfusion, the use of intravenous immunoglobulin; 3) characteristics of readmission for hyperbilirubinemia in 28 DOL: readmission for hyperbilirubinemia in 28 DOL, postnatal age when readmitted, TCB/TSB levels when readmitted

Exposures and measurements:

1. Early postnatal (≤72 hours) ETCOc levels
2. ETCOc levels within 14 days after birth
3. ETCOc levels before each phototherapy and/or exchange transfusion treatment
4. ETCOc levels when stopping phototherapy and/or exchange transfusion treatment

Covariates and characteristics: covariates will be collected including maternal and prenatal history (e.g., mother's blood type [ABO and Rh type], G6PD deficiency status, etc.), family history (e.g., history of hemolytic diseases in the previous newborn, history of NHB treatment in the previous newborn, etc.). Clinical characteristics include demographic characteristics (e.g., gestational age, birth weight), infant's blood type (ABO and Rh type), the status of G6PD deficiency,ABO incompatibility and hemolysis, feeding history and other risk factors (e.g., early discharge after birth, excessive weight loss and the presence of hematoma) as well as data related to the primary and secondary outcomes.

For analysis, this study will examine the association between early postnatal ETCOc and the incidence of hemolytic hyperbilirubinemia, and the relation of ETCOc levels with the characteristics of treatments for hyperbilirubinemia.

Inclusion Criteria:

• Infants who are born at gestational age ≥35 weeks and with a birth weight ≥2000 grams within 72 hours after birth
• Infants who are born at study centers
• Infants with the informed consent obtained from the parents or legal guardians

Exclusion Criteria:

• Immediate requirement of respiratory support after birth (e.g., mechanical ventilation, nasal high-flow cannula oxygen therapy)
• Mothers who have active tobacco smoking or continuous environmental tobacco exposure during pregnancy
• Major congenital anomalies (e.g., cardiac or lung abnormalities, lethal chromosomal defects)
• The presence of injury of nasal mucosa, choanal atresia or Pierre Robin Sequence

The eligible study population will be screened in the well-baby nursery or the neonatal intensive care unit (NICU).

There is not a plan to make individual participant data available.