Women of childbearing age have a high prevalence of iron deficiency and iron deficiency anemia. Iron deficiency before pregnancy can lead to premature delivery, fetal growth restriction, low birth weight of newborns and iron deficiency anemia during pregnancy. Therefore, pregnant women should often eat animal food with high iron content and high utilization rate, and those with iron deficiency or iron deficiency anemia should correct anemia before pregnancy. Iodine is an indispensable trace element in the synthesis of thyroid hormone. In order to avoid the adverse effects of iodine deficiency during pregnancy on fetal intelligence and physical development, pregnant women should not only choose iodized salt, but also take 1 time of iodine-rich seafood every week. Folic acid deficiency can affect the proliferation and differentiation of embryonic cells and increase the risk of neural tube malformation and abortion. Pregnant women should supplement 400 μg folic acid every day from the third month before pregnancy and continue throughout pregnancy.

(2) Key recommendations

1. Eat more foods rich in iron to increase the body's iron reserves;

2. Choose iodized salt and eat more foods rich in iodine;

3. Start folic acid supplementation at least 3 months before pregnancy.

(3) Practical application

1. Eat foods rich in iron: the iron content and iron absorption rate in animal blood, liver and red meat are high, and there should be 50~ 100 g of lean animal meat in three meals a day, and 25~50 g of animal blood or livestock liver and kidney once a week. The absorption and utilization of dietary iron can be improved by ingesting meat or blood and liver rich in iron and vegetables and fruits with more vitamin C.

2. Choose iodized salt and eat foods rich in iodine: Because of the general lack of iodine in food, choosing iodized salt can ensure regular iodine intake [1 1]. At present, the amount of iodized salt in China is 25 mg/kg, and the cooking loss rate of iodine is 20%. According to the daily salt intake of 6 g, the iodine intake can be about 120? G/d, reaching the recommended amount for adults. Considering the increasing demand for iodine during pregnancy, the serious harm of iodine deficiency to the fetus, and the pregnancy reaction in early pregnancy will affect the intake of food and iodine, it is suggested that pregnant women should take 1 time of iodine-rich food, such as kelp, laver and mussel, in addition to regularly eating iodized salt, in order to increase a certain amount of iodine reserves.

3. Supplement folic acid three months before pregnancy: Folic acid in natural food is polyglutamic acid with complex structure. After entering the body, it must be decomposed into small-molecule monoglutamic acid before it can be absorbed by the small intestine. The bioavailability is about 50%, and the loss rate of cooking and processing can reach 50%~90% because it is sensitive to heat, light and acid. The synthetic folic acid supplement is folic acid monomer, which has good stability and can be directly absorbed by the intestine. The bioavailability of taking it on an empty stomach is 100%, and that of mixing it with diet is 85%, which is 1.7 times that of natural food folic acid. Therefore, pregnant women should supplement 400 μg folic acid every day.

(4) Scientific basis

1. Iron deficiency or anemia affects the success of pregnancy and the health of mother and child: The amount of iron stored in normal adult women is about 0.3~ 1.0 g, but women of childbearing age are often short of iron reserves due to childbirth and menstrual blood loss. Iron deficiency or anemia in pre-pregnancy and early pregnancy can affect the pregnancy outcome and the health of both mother and child, lead to abortion, fetal growth restriction and low birth weight of newborns, and make pregnant women more prone to iron deficiency anemia during pregnancy [12- 13]. Anemia in pregnant women leads to insufficient iron storage in fetal liver, which not only affects the synthesis of hemoglobin in early infants and causes anemia, but also affects the synthesis of iron-containing enzyme (heme) and the production of dopamine D2 receptor in the brain, which has an irreversible impact on the intellectual and behavioral development of fetuses and newborns [14]. Because the demand for iron during pregnancy is significantly increased, and good iron nutrition is a necessary condition for successful pregnancy, women of childbearing age should take as much animal food rich in iron as possible from the beginning of planned pregnancy to reserve enough iron for pregnancy; Women who are pregnant but have anemia or iron deficiency should be treated actively and then get pregnant after anemia or iron deficiency is corrected.

2. The nutritional status of iodine is related to the intelligence and physical development of offspring: the iodine in human body is mainly stored in thyroid gland, about 8~ 15 mg, which can maintain the body's needs for 2~3 months. Iodine deficiency causes the decrease of thyroid hormone synthesis and hypothyroidism, which further affects metabolism and protein synthesis, and causes irreversible damage to children's intellectual development. The World Health Organization (WHO) estimates that iodine deficiency causes children's intellectual loss by 5-20 IQ scores, and the domestic estimate of children's intellectual loss is 10~ 15 percentage points [ Studies have shown that cretinism can occur in newborns when women's iodine intake is less than 25 μg/d before and during pregnancy. Failure to supplement iodine in time during pregnancy will increase the risk of fetal nervous system development retardation, and the benefits of iodine deficiency patients in the first trimester of pregnancy are obviously greater than those in the third trimester. Good iodine nutrition before and during pregnancy can prevent the adverse effects of iodine deficiency on fetal nervous system and physical development [16].

3. Folic acid supplementation in the first three months of pregnancy can reduce the risk of neural tube and various malformations in offspring: Folic acid is one of the main donors in one carbon unit, which plays an important role in homocysteine metabolism, DNA synthesis and methylation, and is related to normal development, health maintenance and the risk of various diseases, and is an indispensable micronutrient for cell proliferation, tissue growth and body development. Animal experiments and population epidemiological studies show that folic acid deficiency in early pregnancy can cause stillbirth, abortion, brain and neural tube abnormalities, as well as eye, lip, palate, gastrointestinal tract, cardiovascular system, kidney, bone and other organs abnormalities [17].

Embryonic neural tube differentiation occurs in 2~4 weeks after fertilization, that is, 4~6 weeks of pregnancy, and women realize that their pregnancy is usually after the fifth week of pregnancy or later. At this time, it is undoubtedly too late to supplement folic acid to prevent fetal neural tube malformation. Studies have shown that the folic acid deficiency in women of childbearing age has been improved to some extent after 400 μg folic acid supplementation every day for 4 weeks, and the serum or plasma folic acid concentration has reached an effective level and a stable state after continuous supplementation of 12~ 14 weeks [18]. Therefore, 400 μg folic acid (supplement) must be supplemented every day from the third month before pregnancy, so as to ensure a good folic acid nutritional state in the early embryo, meet the needs of neural tube differentiation for methyl, and reduce the risk of neural tube and multiple organ malformation in the offspring; For women who have had a birth history of neural tube malformation and are suspected of folic acid deficiency, a larger dose of folic acid should be supplemented under the guidance of a doctor [19].

The level of folic acid in women of childbearing age in China is low, and the rate of folic acid deficiency in red blood cells is about 54.9% in northern women and 7.8% in southern women. There are still quite a few women of childbearing age who lack folic acid in areas with low incidence of fetal neural tube defects. The average incidence of neural tube defects in China is 2.74‰ (about 7‰ in the north and about 1.5‰ in the south), and the northern region is higher than the southern region, and the rural region is higher than the urban region, with about 80 8~ 10/00000 children born each year. Many human folic acid intervention experiments at home and abroad have confirmed that folic acid supplementation during embryonic neural tube differentiation can effectively reduce the incidence of fetal neural tube malformation, and taking folic acid supplementation from pre-pregnancy to early pregnancy can prevent 80% of neural tube malformations from being born; Supplementing folic acid to mothers who have given birth to neural tube malformations can reduce the rate of neural tube malformations by 70% in their next pregnancy. A large-scale community intervention experiment in China showed that the prevention rates of neural tube defects in areas with high incidence and low incidence of neural tube defects reached 85% and 4 1% respectively when women took folic acid 400 μg every day before and after pregnancy.

In China, it has become an important nutrition intervention policy to supplement 400 μg folic acid (supplement) to pregnant women and pregnant women every day.