[Levels of human milk oligosaccharides in breast milk of mothers delivering preterm infants of different gestational ages and their effects on early growth and development].

Objective: To investigate the human milk oligosaccharides (HMOs) levels in breast milk of mothers delivering preterm infants and their effects on the early growth and development of infants. Methods: In this prospective cohort study, full-term and preterm newborns whose parents decided to breastfeed were recruited from Peking University Third Hospital between December 1, 2017 and November 30, 2018. The preterm infants were divided based on their gestational ages into extremely preterm (<28 weeks), very preterm (28-31+6 weeks) and moderate to late preterm (32-36+6 weeks) groups. Breast milk was collected from mothers at 7, 14, 28 and 120d postpartum. 368 breast milk samples were collected from 125 mothers in this study, including 54 mothers of full-term infants, 23 mothers of moderate to late preterm infants, 39 mothers of very preterm infants, and 9 mothers of extremely preterm infants. Ultra-performance liquid chromatography-mass spectrometer (UPLC-MS/MS) was used to determine the concentration of 2'-fucosyllactose (2'FL), 3-fucosyllactose (3FL), 3'-sialyllactose (3'SL), A-tetrasaccharide (P1), lacto-N-tetraose (LNT), lacto-N-neotetraose (LNnT), lacto-N-fucopentaose Ⅱ (LNFP-Ⅱ) and lacto-N-fucopentaose Ⅴ (LNFP-Ⅴ). Secretor status of mothers was defined as 2'-fucosyllactose (2'FL) concentration in colostrum and transitional milk greater than 200 µg/mL. Weight gain and the occurrence of allergic diseases of infants were collected at 120 d(4 months) postpartum. The chi-square test or the Fisher's exact test was used for the comparison of categorical data between groups; Kruskal-Wallis test and Wilcoxon rank sum test were used for comparison of continuous data between groups. Nemenyi test was used for multiple comparison. Results: 79.2% (99/125) of the mothers were secretor. There were no statistical differences between groups in the secretor status of mothers (χ²=1.31,P>0.05). The total concentration of HMOs peaked at 1-2 weeks postpartum. Compared to the preterm milk, the HMOs from the term milk was trending downwards at an earlier time. In the breast milk of secretor mothers on 28 d, total concentration of HMOs significant differed among the three groups of preterm milk and the term milk, with the median value of 4 587.09,4 615.25,5 277.44,5 476.03 µg/mL, respectively (Kruskal-Wallis χ²=8.1234,P=0.044). When analyzed by the median weight gain of the infants (low vs high weight gain) at 4 months postpartum, 2'FL was significantly lower in the high weight gain group at 7 d (1 818.04 µg/mL vs 2 181.67 µg/mL, W=1 386,P=0.018), while LNT & LNnT were significantly higher (1 182.36 µg/mL vs 1 053.62 µg/mL, W=816,P=0.044). The level of 3FL at 120 d was significantly affected by presence of allergic disease in infants, breast milk from mothers of infants with allergic disease had lower 3FL than those from mothers of infants without allergic disease (256.17 µg/mL vs 286.18 µg/mL, W=564,P=0.026). Conclusions: The overall profiles of HMOs in breast milk of mothers delivering preterm infants was basically the same as that of mothers delivering term infants; individual HMOs play a role in weight gain and the development of allergic diseases in preterm infants, but the mechanism is unclear and needs further study.