Objective: The objective of this study was to assess the predictive performance of preoperative cervical length (CL) for delivery within 1 week after pleuroamniotic shunting (PAS) in fetuses with severe hydrothorax. Methods: A prospective cohort of fetuses with severe hydrothorax referred to our fetal surgery center in Querétaro, Mexico from January 2012 to July 2020. Severe fetal hydrothorax was diagnosed as an accumulation of fluid within the fetal pleural space accompanied with severe bilateral lung compression, mediastinal shift, polyhydramnios, and/or hydrops. Transvaginal CL was measured immediately before PAS, and a short cervix was defined as that <25 mm. The interval from fetal intervention to delivery, prevalence of preterm prelabor rupture of membranes (PPROMs), and associations with delivery within the first week after PAS according to a short or a normal CL, were evaluated. Results: Thirty-five pregnancies with severe fetal hydrothorax treated with PAS were evaluated. Median gestational age at PAS was (weeks + days) 31+2 (range, 26+0–36+1). Two (5.7%) and 7 (20.0%) cases delivered within the first 24 h and 1 week after PAS, respectively. Ten (28.6%) women had a short cervix before PAS, while 25 (71.4%) had normal preoperative CL. Women with a short cervix showed lower mean interval between fetal intervention and delivery (2.4 vs. 5.5 weeks, p = 0.01), and higher prevalence of PPROM (50 vs. 12%, p = 0.01), as compared to women with a nonshort cervix. Preoperative short cervix was associated with significantly higher risk of delivery within the first 24 h (20.0 vs. 0%, respectively, p < 0.05) and 1 week after PAS (50.0 vs. 8.0%, respectively, p < 0.01) compared with pregnancies with normal preoperative CL. Conclusion: In pregnancies with severe fetal hydrothorax candidates for pleuroamniotic shunt, identification of a short cervix before fetal intervention can predict delivery within 1 week after the surgical procedure.