Other: Control group

Conventional treatment: Neonates will be placed in an incubator (Ningbo David Medical Device Co., LTD, XHZ model) at 30℃ and relative humidity at 55%. Throughout the study, exclusive breastfeeding and professional care will be provided for the newborns. Newborns requiring phototherapy receive it in the following manner: Phototherapy eye masks (Foshan Forman Medical Technology Co., LTD., Yuesun Mechanical Equipment No. 20160015) and phototherapy diapers (Foshan Baojusheng Medical Equipment Co., LTD., GB/T33280) will be used to cover the eyes and perineum, respectively. Phototherapy was provided via LED blue light continuous irradiation with a wavelength of 425-475nm. All treated neonates will receive continuous phototherapy for 12 hours, then allowe to rest for 6-8 hours, then receive another 12 hours of continuous phototherapy. The decision to continue with further treatment depends on changes in the neonate's jaundice.

Experimental: Sunbathing group

The sunbathing group will receive all interventions prescribed for the control group and assign to sunbathing (placement in a bed next to a sunny window) after birth for one week according to the following plan: Every morning and afternoon neonates will sunbath for 0.5 to 1 hour to avoid excess sun exposure. Healthcare workers will guide and assist families in their preparations. The caregiver will place a black eye patch on the infants to protect the retina, and a cloth will be wrapped around the hands and feet to prevent scratching, but care will be taken that the wrap is not too tight to avoid circulation disorders. Baby boys will have their genitals covered to protect them from sun damage. After feeding, the newborn will be placed on a sunny platform with fully exposed skin and frequent position changes, while the glass of the window prevent injury from UV light exposure.

Experimental: Bifidobacterium group

The newborns in the Bifidobacterium group will receive all interventions prescribed for the control group, and also be assigned to orally be given Bifidobacterium triple viable powder (Shanghai Xinyi Pharmaceutical Company, Peifeikang powder, 0.5 g/dose, 3 times/day. Bifidobacterium triple viable powder contains live bacteria of long Bifidobacterium at no less than 1.0 × 107 CFU/g, stored at 2.8℃ away from light) beginning within 24 hours after birth and continuing for 1 week. No sunbathing will be prescribed.

Experimental: Combination group

The combination group will receive all interventions of both the group sunbathing and the Bifidobacterium group as well as all interventions prescribed for the control group.