The article describes a case of unexpected perinatal death of a stillborn child caused by a rare mutation of the MTM1 gene. There were no abnormalities during labor, electronic fetal monitoring showed no signs of fetal distress, but the baby was born without crying, with poor muscle tone and pale skin. Conventional prenatal tests did not detect the mutation, so whole-exome sequencing was performed, which revealed a hemizygous variant of the MTM1 gene. Genetic mutations can lead to miscarriages, perinatal deaths and abnormalities in fetal development, but are not routinely tested for without a family history. Whole-exome sequencing testing has the potential to identify such hidden causes that are missed by non-invasive prenatal testing or analysis of chromosome copy number variants. Indications for this test in pregnant women require further discussion.