There are more types of birth control injections that women can use, which need to be combined with the specific clinical condition of the patient and the type of birth control injections to determine the specific time of medication. 1.Premature miscarriage: if there is pain in the lower abdomen, little vaginal bleeding and low progesterone value, it is mostly considered to be related to the insufficient function of ovarian corpus luteum, resulting in the decrease of progesterone level in the body, which usually needs to be applied until about 1 week after the symptoms disappear, or 3 months after the formation of placenta The progesterone supplementation is no longer needed; 2, preterm labor: 28 weeks of gestation after the appearance of contractions or red, for preterm labor performance. Preferred magnesium sulfate intravenous drip, to protect the fetal nervous system, magnesium sulfate can not be used for more than 1 week, due to the use of too long easily caused by calcium deficiency, so generally about 3-5 days need to stop the drug. When contractions are difficult to suppress, ritodrine injection or other drugs will be chosen for fetal preservation, which can be used for 1-2 weeks, and when contractions are significantly suppressed, the drugs can be stopped according to the specific situation. During the period of fetal preservation, pregnant women should pay attention to rest, avoid strenuous activities or physical labor, keep a relaxed mood, no need to be overly nervous, and conduct regular maternity checkups to deal with abnormalities in time to ensure the healthy development of the fetus.