Objective To compare the effects of different doses of vitamin D supplementation on vita-min D deficiency and insufficiency in premature infants.Methods A total of 126 premature infants hospital-ized in the pediatrics department of this hospital from March 25,2021 to December 30,2022 were selected as the study subjects and began to supplement different doses of vitamin D on 3 d after birth under the intestinal tract tolerance.They were divided into 500,900 and 2 100 IU/d groups according to vitamin D supplementary dose.The differences in vitamin D levels at beginning and after supplementation were compared among the groups.Results Among 126 premature infants,there were 52 cases of vitamin D deficiency and 74 cases of vi-tamin D insufficiency.Compared with vitamin D insufficiency,the proportion of vitamin D supplementation in the mothers of the premature infants with vitamin D deficiency was lower(P＜0.05).The serum calcium,phosphorus,alkaline phosphatase and 25-hydroxyvitamin D levels after birth had no statistical difference a-mong 3 groups(P＞0.05).The 25-hydroxyvitamin D level after supplementation had statistical difference a-mong 3 groups(P＜0.05),moreover the 500 IU/d group was lower than the 2 100 IU/d group(P＜0.05).The longest duration of vitamin D supplementation in the 2 100 IU/d group was 90 d,its highest 25-hydroxyvitamin D level after supplementation was 48.3 ng/mL,no vitamin D poisoning condition appeared,there were still 40 cases(85.1％)of vitamin D deficiency and insufficiency after supplementation in the 900 IU/d group,and 17 cases(25.8％)in the 2 100 IU/d group.Conclusion Giving vitamin D 2 100 IU/d in pre-term infants is recommended after birth to prevent the vitamin D deficiency.

Placental and maternal-fetal circulation Doppler ultrasound are the main noninvasive means for maternal-fetal monitoring. However, Doppler studies on placental abnormalities are not well studied yet. Doppler monitoring of the maternal-fetal circulation, involving uterine arteries, umbilical arteries, and fetal vessels, is still used to screen diseases related to placental dysfunction (such as preeclampsia and fetal growth restriction) and to guide clinical management. This article reviews the advances in the clinical application of placental and maternal-fetal circulation Doppler in obstetrics to optimize the clinical management of disorders associated with abnormal placental structure and function.