Cytomegalovirus (CMV) infection is the most common intrauterine infection worldwide, and the clinical manifestations are potentially severe. Typically, the diagnosis of acute CMV infection in pregnancy is based on positive results for maternal IgM. Herein, we present a case of a fetal CMV infection in which maternal CMV-specific IgM antibodies were negative. The patient was a 29-year-old primipara. At 24 weeks’ gestation, fetal ascites, growth restriction (-2.3 SD), and a hyperechoic bowel were detected by ultrasound scan. Fetal anemia was strongly suspected based on the markedly elevated fetal middle cerebral artery peak systolic velocity value at 84.6 cm/s (2.5 MoM). We performed umbilical cord sampling; fetal anemia was mild, but marked thrombocytopenia was noted (hemoglobin level: 9.2 g/dL, platelet count: 28,000/mm3). Maternal blood tests for IgM against TORCH revealed negative results. Nevertheless, we strongly suspected congenital CMV infection based on the sonographic and cord blood examination findings. PCR using amniotic fluid drained at 25 weeks and 3 days revealed CMV-DNA, at which point a definitive diagnosis of congenital CMV infection was made. The condition of the fetus deteriorated, and at 26 weeks and 2 days, fetal death was noted. Pathological examination of the placenta after stillbirth revealed CMV placentitis. This case suggests that maternal CMV-specific IgM antibodies are not reliable for excluding CMV infection in cases of fetal infection with characteristic sonographic findings.