Metformin has been used for more than 20 years as an adjunctive drug in women with polycystic ovary syndrome (PCOS). Metformin is a hypoglycemic agent that has the effect of enhancing insulin sensitivity and reducing the absorption of sugar in the intestine. Patients with polycystic ovary syndrome are often accompanied by insulin resistance, which is thought to contribute to ovulation disorders in women. The most widely used insulin-sensitizing drug for the treatment of anovulation is none other than metformin, which has been shown in numerous studies to be effective in improving ovulation in women with PCOS. Also, some studies have shown that PCOS patients taking metformin can reduce the incidence of ovarian hyperstimulation (OHSS) (Costello et al., 2006), while metformin has also been reported to reduce the rate of miscarriage in PCOS patients. In male infertility patients, diabetes and hyperinsulinemia can directly or indirectly affect sperm quality, leading to increased abnormal morphology of sperm, etc., and studies have shown that metformin-treated men with hyperinsulinemia can improve sperm quality (Bosman E et al., 2015) and help to reduce body weight. In obese patients, metformin seems to provide additional benefit, as one study compared patients with a body mass index (BMI, weight KG/height m2) ≥30 with normal weight patients and found that metformin administration for 6 weeks significantly reduced weight and testosterone levels and improved metabolism-related indicators and insulin sensitivity in obese patients, but had no significant effect in patients with normal weight. The main side effects of metformin are nausea and vomiting, which occur in 20% of patients. If symptoms persist after reducing the dose, discontinuation of the drug should be considered. The importance of vitamin D for fertility has been described in detail in previous articles, in short, vitamin D is closely related to the production of reproductive hormones (including androgens, estrogen and progesterone) and vitamin D deficiency can lead to abnormal sex hormone levels and increase the risk of endometriosis and uterine fibroids, etc. Serum vitamin D product levels are significantly lower in patients with PCOS and supplementation can correct hyperandrogenemia in PCOS and improve reproductive outcomes in patients. In male patients, vitamin D receptors are present in testicular tissue and sperm and affect sperm quality, and supplementation with vitamin D can play a role in protecting reproductive function. The use of adjuvant medication requires the clinician to evaluate the patient’s individual condition and laboratory test results and then use the medication according to the condition, so the moms-to-be must follow the doctor’s instructions and use it on time and in the right amount.