The failure of non‐invasive prenatal testing due to maternal dermatomyositis

We experienced a case of a pregnant woman who failed to obtain a result from NIPT, due to the high level of total cell‐free DNA. A subsequent ultrasound examination discovered that the fetus had severe intrauterine growth restriction, so the woman decided to abort the baby. At the same time, the woman developed slight swelling and tenderness of the proximal interphalangeal and meta‐carpophalangeal joints. At first, these symptoms were not noticed, but, when the pregnant woman was admitted to the hospital, her laboratory tests were seriously abnormal, such as serum lactate dehydrogenase (640U/L), creatine phosphor kinase (4525U/L), kinase isoenzyme MB (170U/L), and a hydroxybutyrate dehydrogenase (398U/L). The patient had no other symptoms at this time. Misoprostol and subsequent forceps curettage were used for the induced abortion, a 167‐g female fetus was aborted. Fetal skin tissue was taken for chromosomal microarray analysis (CMA) and placenta (biopsied in four places and tested as two composite samples) were taken for postnatal karyotyping to exclude a confined placental mosaicism, chromosomal microarray analysis of the fetal skin tissue revealed that the karyotype was 46, XX, karyotyping of placenta (100 cells) gave results of 46, XX, no abnormalities were detected. Ten days after induction, the patient had developed progressive symmetric muscle weakness in the proximal extremities. Physical examination revealed Gottron's sign and erythema. A manual muscle test showed weakness of the muscles (4/5) of her proximal extremities. Electromyography showed myogenic impairment. After excluding the possibility of neoplasia, the patient was diagnosed with dermatomyositis. What's already known about this topic? The reasons for NIPT failure mainly include low values of cell‐free fetal DNA or high values of total cell‐free DNA, and the mechanisms for this have not been completely elucidated. What does this study add? We report a case of a 29‐year‐old pregnant woman who failed to obtain a result from non‐invasive prenatal genetic testing (NIPT) due to maternal dermatomyositis.