Low thyrotropin is a thyroid-related disorder, and Down’s syndrome screening is for chromosomal abnormalities and open neural tube malformations, which are not related. 1. Low thyrotropin is mainly caused by hyperthyroidism and iodine deficiency: (1) Hyperthyroidism: generally due to excessive secretion of thyroid hormones in the patient’s body, as well as hereditary factors, physiological hyperthyroidism caused by pregnancy, and so on. After diagnosis, treatment should be carried out under the guidance of the doctor. (2) Lack of iodine: It may be due to the environment where the patient lives, such as soil or water with low iodine content, or low protein in the body, which affects the absorption and utilization of iodine. On the other hand, both the pregnant woman and the fetus need iodine after pregnancy, and if no attention is paid to replenish iodine, it will result in the lack of iodine in the body, which will cause a certain impact on the nerves of the fetus’ brain. 2. Down’s syndrome screening is to screen for chromosomal abnormalities and open neural tube malformations: it mainly includes trisomy 18, trisomy 21, and screening for the risk of neural tube developmental malformations. Down’s syndrome screening is a safe and convenient test that involves drawing blood from a vein of the pregnant woman and does not cause any harm to the woman or her fetus. If the Down’s syndrome screening test indicates a high or critical risk, further testing is required, such as amniocentesis or non-invasive DNA, to determine whether the fetus has a chromosomal abnormality.