What is safe and what is dangerous when taking medication during pregnancy? Let’s start with an “all or nothing” benefit, which means that within 2 weeks from fertilization, the effect of the medication on the embryo will either cause the child to miscarry, or it will have no effect on the embryo, and the child will have no problems at all. Fertilization usually occurs in the middle of menstruation, if menstruation is once every 28 days, then the all or nothing benefit is probably within one month of menstruation, if the drug is taken without knowing that you are pregnant, you don’t have to be too nervous, and if the child survives then there is usually no problem. Then, after 2 weeks, whether the drug has any effect on the child, we will probably need to understand the U.S. Food and Drug Administration (FDA) classification of drugs for pregnancy. To say whether a drug has an effect on an embryo, you need to look at its results in animal testing and human studies.The FDA categorizes all drugs into classes A/B/C/D/X. Class A controlled studies have not found a risk to human fetuses in early pregnancy (and there is no evidence of risk in mid- to late-gestation), and the likelihood of damage to the fetus appears to be small. Category B Animal reproduction studies did not find a risk to the fetus, and there were no controlled studies in human pregnant women at the time; or Animal reproduction studies showed adverse effects (not just reduced fertility) but these were not confirmed in controlled studies in human women during early pregnancy (and there was no evidence of risk in mid- to late-gestation). Category C Animal studies show adverse effects on the fetus (teratogenic effects or embryocidal effects, etc.) but there are no controlled studies in human women or there is no information from human and animal studies, and the drug should be used only if the potential benefit to the fetus outweighs the potential risk. Category D There is conclusive evidence of risks to the human fetus, but these risks are acceptable for the benefit of the pregnant woman (e.g., use of the drug in a life-threatening situation, or when the condition is so severe that a safe drug cannot be used or a safe drug is ineffective) Category X Animal or human studies have shown the presence of fetal malformations or human experience has shown a risk to the fetus or both, and the risk of the drug is clearly greater than any possible risk when used in a pregnant woman. The risks of the drug clearly outweigh any possible benefits. The drug is contraindicated in pregnant women or women who may become pregnant. Almost any drug can be searched for its FDA classification, and knowing the classification makes it easier to answer the patient’s question. For example, a friend told me that she had irregular periods, found out she was pregnant at 40 days after her menstrual period stopped, and took Furadantin tablets for a urinary tract infection at about 35 days, and asked if it was okay to go ahead and have a baby. Because of irregular menstruation, you can use ultrasound to determine the gestational week first, if the actual gestational week is less than 4 weeks (we calculate the gestational week from the last menstruation), then there is no problem, if we don’t know the current gestational week, or if it is currently more than 4 weeks, then we need to look up the classification of gestational period of furadandine. I checked the domestic data, and I did not find any FDA pregnancy classification for Furadantin, which is indicated by “caution” in the drug insert. I used the English name Nitrofurantoin to search Google, and found that the result is Pregnancy Cat. is B, so it does not matter whether she is within 2 weeks of the embryo is not too important, class B drugs in the whole pregnancy is safe.