Objective The research was performed to investigate the relationship between serum 25-hydroxyvitamin D (25(OH)D) levels and the risk of adverse pregnancy outcomes. Methods We enrolled females who were in the first trimester of pregnancy and had arranged antenatal care at the Weifang Maternal and Child Health Hospital between January 2017 and December 2019. The liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was used to detect serum concentrations of 25(OH)D. The health status of the expectant mothers and fetuses and the incidence of adverse pregnancy outcomes of newborns were monitored through the outpatient, prenatal, and delivery stages in the hospital. Results An initial total of 6 770 females were signed up, while 4 997 females were eventually included. The median value of 25(OH)D concentration was 15.40 ng/mL, and the incidence rate of vitamin D deficiency [25(OH)D < 20 ng/mL] was 71.26%. The occurrence rates of gestational diabetes mellitus (GDM), pre-eclampsia, premature rupture of membranes (PROM), oligohydramnios, polyhydramnios, cesarean delivery, spontaneous abortion or stillborn fetus, fetal malformation, premature delivery, fetal macrosomia, low birth weight, small for gestational age infant, and asphyxia of newborn were 28.31%, 2.27%, 23.47%, 12.68%, 0.51%, 45.71%, 1.44%, 0.93%, 9.26%, 5.05%, 11.68%, 2.68%, 3.18%, and 1.16%, respectively. After adjusting for age, parity, season, pre-existing hypertension, pre-existing diabetes, and vitamin D supplementation, no relationship between 25(OH)D levels and adverse pregnancy outcomes was found (P>0.05). Conclusions Levels of 25(OH)D do not affect the risk of adverse pregnancy outcomes in females during the first trimester of pregnancy.