If a pregnant woman has low thyroid stimulating hormone, it may have effects on the fetus, such as causing low birth weight, premature birth, and miscarriage. However, if it is physiologically low in early pregnancy, there may be no effect. Generally, a low thyroid hormone level in early pregnancy is a normal physiological phenomenon, and it will gradually return to normal in the middle and late pregnancy. However, if the low thyroid hormone level is still abnormal after 20 weeks or if the low level is more, it is an abnormal condition and may be hyperthyroidism, which should be treated as hyperthyroidism to avoid affecting the fetus and leading to malnutrition and miscarriage of the mother and baby. If a pregnant woman has low thyroid stimulating hormone after pregnancy, she should pay attention to it and eat less seafood, such as seaweed, nori and sea fish, and eat more fresh fruits and vegetables.