Background Twin pregnancy is predisposed to a high risk of preterm birth due to cervical insufficiency or structural abnormalities (e.g., "U"-shaped dilation of the cervical canal), posing significant challenges in clinical management.

Objective To investigate whether cervical cerclage should be performed in pregnant women with "U"-shaped dilated cervix during twin pregnancy, and provide reference for the management of similar cases.

Methods The diagnosis and treatment process and pregnancy outcome of conservative treatment of 2 cases of assisted reproductive twin pregnancy with cervical "U"-shaped dilation was reported.

Results Case 1: The pregnant woman was 33 years old, with 1 pregnancy and 0 births. At 20⁺⁵ weeks of gestation, ultrasound showed that the cervical canal was shortened for 3 days, the length of the closed segment of the internal opening of the cervix was about 1.5 cm, and the internal opening was enlarged in a "U" shape. During hospitalization, the pregnant woman was instructed to stay in bed, metronidazole tablets were placed in the posterior fornix of the vagina, half dose of low molecular weight heparin sodium was given to prevent lower limb vein thrombosis, ritodrine hydrochloride injection and atrosiban acetate injection were alternately used to inhibit uterine contractions. Brain protection of magnesium sulfate injection and progesterone soft capsule were placed in the posterior fornix of the vagina. Two infants were delivered by cesarean section at 37⁺¹ weeks of gestation. Case 2: The pregnant woman was 39 years old, with 1 pregnancy and 0 births. At 25⁺¹ weeks of gestation, the ultrasound showed that the cervical canal was "U" shaped dilation, the width of inner vaginal opening was about 2.3 cm, the width of outer vaginal opening was about 0.5 cm, and the dilation length was about 3.1 cm. During hospitalization, the pregnant woman was instructed to stay in bed, given magnesium sulfate injection for brain protection, dexamethasone sodium phosphate injection for promoting fetal lung maturation, and progesterone soft capsule was placed in the posterior vaginal fornix. Two infants were delivered by cesarean section at 36⁺⁵ weeks gestation. Current follow-up showed that all babies were healthy.

Conclusion For pregnant women with twin pregnancies conceived via assisted reproduction complicated by "U"-shaped cervical canal dilation, effective prolongation of gestational weeks and achievement of near-term delivery can be achieved through multidisciplinary comprehensive management—including bed rest, tocolytic agents, progesterone supplementation, anticoagulation therapy, and antenatal corticosteroids for fetal lung maturity—under conditions where the cervical external os remains incompletely dilated, there is no evidence of infection, and uterine contractions are controllable.