A 29-year-old nulliparous woman with polycystic ovary syndrome and no history of ovarian cyst was admitted to obstetric clinic for prenatal screening at 20-week spontaneous gestation of twins. An ultrasound examination showed multicompartmental cysts whose diameters were 20 cm and 15 cm on the left and right ovaries, respectively. A cancer antigen 125 (CA-125) test showed an elevated level of 209.0 U/mL, and the level of alpha fetoprotein (AFP) was 170.0 ng/mL. A diagnosis of physiological cysts was considered. Then, the woman was conservatively managed, and cesarean delivery was scheduled. The size of the cysts increased gradually with the week of gestation, and the diameters got their maximum at 30 cm and 20 cm for each side until 30 weeks (Fig. 1). Unfortunately, she presented spontaneous premature labor then. No adverse maternal or neonatal outcomes were reported. At her 2-month check after delivery, the CA-125 and alpha fetoprotein decreased to normal range. Nevertheless, 6 months after delivery, the sizes of the ovaries were still 20 cm and 10 cm in diameter at the left and right sides, respectively, accompanied by intermittent abdominal pain. Subsequently, she underwent single-port laparoscopic oophorocystectomy (Fig. 2). Pathological analysis revealed bilateral corpus albicans (Fig. 3). The patient recovered smoothly. We present a case of physiological ovarian cysts of unusual size during pregnancy with elevated CA-125, resulting in premature delivery. Expectant management may be considered for giant lutein cyst in pregnancy. However, if there is any suspicion of a malignancy or complications caused by cysts, ovarian cystectomy during pregnancy should be performed.Fig. 2Laparoscopy revealed the huge polycystic ovaries. (A) The pelvis was filled with giant cysts. (B) The left ovary (yellow arrow) was squeezed by the cysts.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Fig. 3The pathologic photomicrograph revealed corpus albicans.View Large Image Figure ViewerDownload Hi-res image Download (PPT) The authors thank Lei Pan and Kui Li, who aided in data collection and image production.