Heparin shots do not enlarge the fetus. Heparin is a Class B drug for pregnant women, which usually refers to a class of drugs that will not affect the development of the fetus, so the fetus will not be oversized by taking heparin. Heparin, as an anticoagulant, is commonly used clinically for thromboembolic disease, myocardial infarction, cardiovascular surgery, extracorporeal circulation, hemodialysis and so on. Heparin is a drug often used by pregnant women to inhibit thrombosis and play an anticoagulant role. For some pregnant women with thrombophilia or rheumatoid immune diseases, heparin is usually required throughout pregnancy. It should be noted that the use of heparin is prohibited for those who are allergic to heparin, those who have delayed blood coagulation, those who have a tendency to bleed spontaneously, those who have ulcerative diseases, and those who have severe hepatic insufficiency, and that patients may experience adverse reactions such as elevated aminotransferases, hematomas at the site of injection, hemorrhages in various mucous membranes, and blood accumulation in joint cavities. The drug should be used under the guidance of a doctor, do not use without authorization to avoid delay.