What is this study about? This study aims to find out the best timing for a major surgery called Kasai portoenterostomy (Kasai surgery) in infants with a liver disease called biliary atresia. The investigators want to see if having the surgery earlier leads to better long-term health for the baby's own liver.

Why is this important? Doctors know that early surgery is important, but it's unclear exactly how early is best. Some babies have surgery within the first month, others within 2-3 months. The investigators want to carefully compare different time windows to see which one gives the child the best chance to keep their own liver healthy and avoid a liver transplant.

How will the study work?

This is an observational study. The investigators will not change the treatment any child receives. The investigators will enroll about 200 infants from 4-5 children's hospitals in China. The investigators will simply group the infants based on their actual age at surgery:

Group 1: Surgery at 28 days old or younger.

Group 2: Surgery between 29 and 60 days old.

Group 3: Surgery between 61 and 90 days old.

Group 4: Surgery between 91 and 120 days old.

The investigators will then follow all children for 2 years after their surgery.

What will the investigators measure? The main thing the investigators want to see is how many children in each group are alive with their own liver working well 2 years after surgery (without needing a transplant). The investigators will also check many other health factors, like liver function tests, nutrition, growth, complications (like infections), and the costs of care.

What is the goal? The results of this study will help doctors and families make better, evidence-based decisions about the best time to perform this critical surgery for babies with biliary atresia.

Inclusion Criteria:

• Infant age ≤ 120 days at the time of planned surgery.
• Diagnosis of type III biliary atresia confirmed by clinical presentation, laboratory tests (e.g., conjugated hyperbilirubinemia), and imaging studies (e.g., ultrasonography showing absent or abnormal gallbladder, triangular cord sign).
• Scheduled to undergo primary (first-time) Kasai portoenterostomy.
• Legal guardian(s) able to understand and provide written informed consent.

Exclusion Criteria:

• Presence of other severe congenital malformations that significantly impact prognosis or surgical risk (e.g., complex congenital heart disease requiring intervention, syndromic biliary atresia as part of a polymalformation complex).
• Pre-existing evidence of decompensated cirrhosis (e.g., refractory ascites, hepatopulmonary syndrome, or hepatic encephalopathy) prior to surgery.
• Previous history of any liver surgery (including prior Kasai portoenterostomy attempt or liver biopsy via laparotomy).
• Any condition that, in the opinion of the investigator, would make the infant unsuitable for participation or could interfere with the completion of follow-up (e.g., severe concurrent infection, life-limiting non-hepatic disease).

This prospective observational cohort study will enroll approximately 200 infants (age ≤120 days) diagnosed with type III biliary atresia (BA) who are scheduled to undergo their first (primary) Kasai portoenterostomy (KPE). Participants will be recruited from 4-5 pediatric tertiary care centers in China. Enrollment is based on real-world clinical presentation and surgical planning; no study-specific intervention is administered. Infants will be grouped into four natural cohorts according to their actual age at surgery: ≤28 days, 29-60 days, 61-90 days, and 91-120 days. The population will be followed prospectively for 24 months postoperatively to compare long-term outcomes across these surgical timing strata.