Abnormal liver function or cholestasis is the result of multiple factors, include low birth weight, smaller than gestational age, preterm birth, infection, lipid emulsion (LE) in parenteral nutrition (PN), insufficient enteral nutrition (EN) etc. Most are inevitable, but the LEs in PN can be selected. So the investigators compare two LEs, and want to see if the SMOF LE can improve hepatic index in preterm infants.

For preterm infants, especially for very or extremely low birth weight infants, it's impossible to achieve total enteral feeding in short time. So, PN has played an important role to sustain normal life. But, it also has an adverse effect on liver namely parenteral nutrition-associated liver disease (PNALD). LE(s) in PN has been showed to result in PNALD. So changing the type of LEs has been an ideal solution.

Two types of lipid emulsions are currently used for pediatric patients: one LE(the second generation) is composed of 50% long-chain triacylglycerols (LCTs) and 50% medium-chain triacylglycerols (MCTs), prepared from soybean oil and coconut oil respectively. A new LE (SMOF) contains 30% LCTs, 30% MCTs, 25% olive oil, and 15% fish oil. SMOF is rich in omega-3 polyunsaturated fatty acids which derived from fish oil. It may reduce inflammation in premature infants, prevent or treat cholestasis, and reduce oxidative stress.

Because of the different compositions, they have different effect on liver, inflammation, oxidative stress, etc. Therefore, the investigators designed a prospective, randomized and double-blind study to compare the different LEs (MCTs/LCTs and SMOF), so as to select a more suitable fat emulsion for premature infants in order to improve clinical outcomes.

Inclusion Criteria:

• Premature infants (gestational age < 32 weeks) with birth weight < 1500g were admitted to NICU of Xin Hua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China within 24 hours after birth
• No contraindications to parenteral nutrition
• Expected PN support for 14 days or more
• Parents or guardians agree

Exclusion Criteria:

• Parenteral nutrition support was provided prior to enrollment
• EN calorie for 10% or more
• Congenital intestinal structural/functional abnormalities
• Liver function damage caused by viral hepatitis, genetic metabolism and abnormal biliary tract
• Congenital or acquired immunodeficiency
• Complex congenital heart disease