The advantages of low molecular heparin sodium for fetal preservation include higher safety and regulation of immunity, while the disadvantages are side effects such as abnormal liver function and osteoporosis. 1. Higher safety: the bleeding of low molecular heparin is relatively small, which can play a certain role in regulating the pregnant women who have already experienced fetal instability. At the same time, low molecular heparin can improve the blood circulation of pregnant women. In addition, the drug has fewer allergic reactions. 2. Regulate immunity: low molecular heparin sodium has immunomodulation function, which can help inhibit some cell functions and regulate human immunity. 3. Disadvantages: Low molecular heparin sodium has the risk of causing liver function abnormalities, osteoporosis, allergic reactions and other diseases. It is contraindicated in patients with severe coagulation disorders, severe liver and renal impairment, and so on. Low molecular heparin sodium must be used under the guidance of a doctor, if there are allergies and other abnormal symptoms need to consult a doctor in time to avoid accidents, and at the same time, pay attention to rest during pregnancy, at the same time should be relaxed, to avoid nervousness, anxiety, there is any discomfort should be timely to the hospital, by the doctor to clarify the diagnosis and cooperate with the doctor to deal with the symptoms.