DHA has the ability to promote fetal neurodevelopment and is generally more effective when taken after the 4th month of pregnancy. DHA belongs to a kind of nutrient, for long-chain polyunsaturated fatty acids, can promote the development of fetal nervous system and vision, generally in the middle of pregnancy, that is, the fourth month of pregnancy to start taking. At this time, the fetal nervous system is developing rapidly, dividing rapidly and maturing, and it is the time when some complex senses are formed, so supplementing DHA at this time is more effective. There are no clear adverse reactions or contraindications to taking DHA, but care should be taken to use it under the guidance of a doctor. Pregnant women should pay attention to regular pregnancy checkups and screening for Down syndrome to ensure the healthy development of their children. If abnormal symptoms exist, seek medical attention.