Abstract: Gas chromatography-mass spectrometry (GC-MS) was used to determine the dynamic changes of fatty acids in breast milk during different lactation periods. The effects of maternal blood type, childbearing age, pre-pregnancy body mass index (BMI), mode of delivery, gestational age, infant sex and parity on the contents of polyunsaturated fatty acids (PUFAs) directly related to infant growth and development such as linoleic acid (LA), α-linolenic acid (ALA), arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) in mature milk were analyzed. The results showed that the contents of saturated fatty acids (SFAs) in colostrum and mature milk were significantly different (P < 0.05). The content of monounsaturated fatty acid (MUFA) decreased gradually with the prolongation of lactation period, but the difference was not significant (P > 0.05). There was no significant difference in the content of total PUFAs during different lactation stages (P > 0.05). The contents of AA and DHA decreased gradually with the prolongation of lactation; they were not significantly different between colostrum and transitional milk (P > 0.05), but were significantly higher than those in mature milk (P < 0.05). LA content in breast milk was relate to infant sex, ALA content was related to pre-pregnancy BMI, the contents of AA and EPA were related to maternal blood type, the content of DHA was related to pre-pregnancy BMI and maternal blood type; all these correlations were statistically significant (P < 0.05).

Key words: gas chromatography-mass spectrometry (GC-MS), breast milk, fatty acid, polyunsaturated fatty acid (PUFA), factors