Objective?To observe the effects of immediate administration and delayed administration on pregnancy complications, pregnancy outcomes and offspring development in patients with pregnancy complicated with hypothyroidism after diagnosis, to provide reference for clinical prevention and treatment of pregnancy complicated with hypothyroidism. Methods?A total of 400 pregnant women with hypothyroidism who were admitted to Lanzhou Maternal and Child Health Hospital from January 2018 to December 2019 were selected, according to the random number table method, they were divided into early administration group (administration after diagnosis, 200 cases) and delayed administration group (administration 1 week before the expected date of delivery, 200 cases), both groups were treated with medication until delivery; in addition, 200 healthy puerperae with normal thyroid function who delivered in Lanzhou Maternal and Child Health Hospital at the same time were classified as control group. The subjects in the 3 groups were followed up for 1 year after delivery. The thyroid function indexes, pregnancy complications, maternal and infant outcomes, and offspring intelligence and physical development 1 year afterbirth were compared among the three groups of subjects. Results?Compared with the control group, the levels of free triiodothyronine (FT3) and free thyroxine (FT4) in the two groups before and after treatment significantly decreased, and thyroid-stimulating hormone (TSH) levels significantly increased; compared with before treatment, after treatment, the levels of FT3 and FT4 in the two groups significantly increased, but the delayed administration group was significantly lower than the early administration group, TSH levels significantly reduced, but the delayed administration group was significantly higher than the early administration group; the proportions of gestational hypertension, diabetes mellitus, premature rupture of membranes/abnormal amniotic fluid, postpartum hemorrhage, neonatal asphyxia, neonatal death/abortion, intrauterine distress, and fetal growth retardation all showed an increasing trend in the control group, early administration group and delayed administration group; in addition, the proportions of gestational hypertension, premature rupture of membranes/abnormal amniotic fluid, neonatal asphyxia, intrauterine distress and fetal growth retardation in the delayed administration group were significantly higher than those in the early administration group and the control group, the proportions of gestational hypertension, premature rupture of membranes/abnormal amniotic fluid, and neonatal asphyxia in the early administration group were significantly higher than those in the control group; the scores of gross motor development quotient (GMQ), adaptive behavior development quotient (ABQ), language development quotient (LQ), personal social development quotient (ISBQ) and fine motor development quotient (FMQ) of the offspring of the 3 groups of subjects in the control group, early administration group and delayed administration group all showed a decreasing trend, and the delayed administration group was significantly lower than those of the early administration group and the control group; the head circumference, body weight and body length indexes of the offspring of the delayed administration group were significantly lower than those of the early administration group and the control group, the weight and length of the offspring of the patients in the early administration group were significantly lower than those in the control group (all P<0.05). Conclusion?Hypothyroidism during pregnancy will increase the incidence of pregnancy complications and adverse maternal and infant outcomes, and has a direct impact on the recent intellectual and physical development of the patient's offspring, therefore, early aggressive treatment can help improve thyroid function and improve prognosis.