Objectives: To analyze preterm birth related factors for single intrauterine death in monochorionic twins. Design: Retrospective case-control study. Setting: A single medical centre in Shenyang, China, 2012-2018. Sample: preterm delivery with intrauterine fetal death in monochorionic twins (cases, n = 35) were compared with a group of full term birth (controls, n = 4). Methods: Related factors were compared in the two groups and logistic regression was used to adjust for confounding. Main outcome measures: Odds ratio (OR) and 95% confidence interval (CI) for the related factors of preterm birth Results: This study included 39 monochorionic twins following single intrauterine death. The significant risk factor associated with preterm birth is the gestational age of single intrauterine death (OR=1.317, 95% CI: 1.027-1.689). The timing of prolong gestational age shorten with the increasing gestational age of single intrauterine death. We found that in all monochorionic twins cases and spontaneous preterm birth cases, increases in the gestational age at single intrauterine death was associated with shorter prolongation of gestational age in the surviving twin. Conclusions: The gestational age of single intrauterine death was a risk factor of preterm delivery. Increases in the gestational age at single intrauterine death led to a shorter prolongation in gestation of the surviving twin. Funding: This study was funded by Prenatal diagnosis, intrauterine intervention and prognosis evaluation of complicated twins (No. 2018YFC1002902) Tweetable abstract: The gestational age of intrauterine fetal death was a risk factor of preterm delivery. Keywords Gestational age; Prolongation of gestational age; Twin pregnancy；