Mental retardation in children is caused by impaired brain development and poor development of the entire mental activity. It is highlighted by poor learning ability and difficulty in taking care of oneself in daily life. There are many causes of mental retardation in children, mainly the following: i. Genetic Genetic factors are one of the main causes of severe mental retardation. It is reported that in developed countries, mental retardation due to genetic disorders accounts for more than half of the total number of severe mental retardation. In addition, there is a type of mental retardation without clinical abnormal findings. This type of mental retardation is generally considered to be the result of the interaction of polygenic and non-medical biological environmental factors, and is therefore also known as “socio-cultural” or “socio-psychological” mental retardation. This is also known as “socio-cultural” or “socio-psychological” mental retardation. The prevalence of this type of mental retardation without abnormal clinical findings has the following characteristics: (1) the poorer the socioeconomic and cultural-educational conditions, the higher the prevalence in the population; (2) the prevalence is low in preschool, increases rapidly in school age, and peaks in adolescence; and (3) the children with this type of mental retardation are more concentrated in families where the mother is mentally retarded. In recent years, it has been found that some minor chromosomal abnormalities can also cause mental retardation, thus making the position of chromosomal abnormalities in the cause of mental retardation more compelling. Second, infections and difficult prenatal causes: This category of causes has been well understood in the late last century and the beginning of this century, and better interventions and treatment measures have been carried out. Infection with rubella virus, influenza and other viral diseases in the first 4 months of pregnancy can cause congenital malformations in the fetus, which are extremely harmful to the fetus and infant and can easily incur congenital malformations and mental retardation. Perinatal causes: 1. Asphyxia: the main factors are hypoxia, prematurity, intracranial hemorrhage and hyperbilirubinemia. There are many causes of cerebral hypoxia, such as placental malfunction, placental abruption, twisted umbilical cord, cord bypass and other causes and various factors that cause intrauterine (or neonatal) asphyxia. The incidence of perinatal fetal asphyxia is 1.2% to 5.3%, and hypoxic encephalopathy is a common neurological lesion in the perinatal period, which generally has a good prognosis, but more severe fetal asphyxia can cause irreversible brain damage, leaving sequelae of varying degrees, such as mental retardation, motor impairment and convulsions. Some studies have shown that asphyxia lasting more than 15 minutes can cause irreversible damage to the pediatric nervous system. 2, weight and head circumference: low birth weight infants are children whose weight at birth is less than 2500g. Researchers have concluded that: low birth weight children are generally worse than normal children in early psychoneurological development, childhood intelligence and learning ability after school. They point out that birth weight is generally predictive of later intellectual development. Studies have shown that: low birth weight (LBW), especially very low birth weight (VLBW), is a major perinatal factor leading to infantile mental retardation. Many studies at home and abroad have consistently shown that malnutrition during pregnancy is one of the main causes of intrauterine fetal growth retardation. Where the mother is malnourished, the physical development of the child is significantly delayed, and this small child is often accompanied by low intelligence, behavioral disorders or other disorders. Fourth, social and family psychological factors early social isolation, artificial emotional deprivation, lack of maternal love, orphans without care, children with severe mental illness, cultural isolation, inappropriate teaching methods, etc. can affect the level of intelligence. Children of high socioeconomic class, stable family structure, or whose mothers were well educated have been shown to have an IQ difference of only 5-7 points between children with maternal disadvantages and controls, while children with low socioeconomic status, unstable families, or mothers who were not well educated have IQs 19-37 points lower than controls. It can be shown that disadvantageous factors at birth by themselves are not very significant for the later physical and mental development of children, but only in combination with adverse environmental and psychological factors. Therefore, it is believed that large families, multiple children, short birth intervals, twins and parental divorce have a direct impact on children’s intellectual development or obstructive effect. V. Environmental factors 1. Geographical environment: iodine deficiency in pregnant women is one of the important factors affecting the normal development of the fetus. 2, noise: the impact of noise on the fetus is mainly manifested in the fetal development, fetal reaction and teratogenic effects. Noise also has a teratogenic effect on human fetus. According to Jones and other reports, from 1970 to 1972 in the Los Angeles International Airport around 90dB (A) and other loud curve noise area born in the baby, the incidence of congenital defects than other areas. Domestic investigation of this also found that women workers exposed to high-intensity noise, the occurrence of congenital defects in the offspring of the control group significantly increased. 3, radiation: research shows that both X-rays or other radiation, can cause embryonic development to stop and then malformations. The extent to which the embryo or fetus is affected by radiation depends on three factors: (1) the type and dose of radiation; (2) the stage of development at the time of exposure; and (3) the sensitivity of the embryo to radiation. 4. Heavy metals: Excessive lead content is prone to infertility, spontaneous abortion, production of low weight babies, and their babies have developmental delays and mental retardation. The method to prevent hypo-energy is mainly to eliminate or avoid it in a targeted way according to the above-mentioned causes. Early detection, early intervention and early treatment of mental retardation are necessary. Parents can refer to the following criteria: a. Can not laugh. Normal children will laugh at 2 months, and can be amused to laugh loudly at 4 months, while children with mental retardation, generally do not laugh, or will only giggle purposelessly; Second, see but not see, hear but not hear. After 6 months of age, he still cannot notice that adults are talking to him. Poor attention to surrounding people and objects, dull gaze; iii. Feeding difficulties. When feeding solid foods such as rice and steamed buns to infants aged 6-8 months, infants often experience nausea and vomiting, poor chewing ability, and frequent choking and coughing; iv. sticking out the tongue and salivating when awake, even extending to 2-3 years of age; v. delayed motor development. still unable to lift the head at 4 months, still unable to sit alone at 10 months, unable to use fingers after 12 months After 1 year of age, the baby still cannot pronounce words purposefully, and sometimes may scream without purpose; vii. Attention is not focused and interest in toys is short-lived; ix. Cannot distinguish between relatives and strangers. X. Much purposeless activity, which is difficult for adults to understand. Of course, if early signs of suspicion are detected, it is important that you consult a doctor for early diagnosis and treatment.