Heparin injections in pregnancy usually have no significant effect on the fetus. Heparin injections during pregnancy usually use low molecular heparin, which is unable to pass through the placental screen and therefore has no effect on the fetus. Heparin is mainly used in the clinic for the prevention and treatment of thrombosis or thromboembolic disease and disseminated intravascular coagulation; it is also used as an anticoagulant for hemodialysis, extracorporeal circulation, surgery and other operations. Pregnant women take heparin mainly to avoid fetal arrest, miscarriage, premature labor and other conditions caused by hypercoagulation of blood during pregnancy. Heparin is mainly contraindicated in people who are allergic to it, have bleeding tendency, delayed blood coagulation, as well as severe liver insufficiency, ulcer disease, trauma, and postpartum bleeding. Although low molecular heparin will not affect the growth and development of the fetus, it should be used under the guidance of a doctor and the liver function and blood clotting function should be checked regularly to avoid bleeding tendency. If any abnormality occurs, please consult a doctor in time for standardized diagnosis and treatment.