A Miscarriage

1. (now rare except in miscarriage of justice) A failure; a mistake or error. [from 16th c.]
2. The spontaneous natural termination of a pregnancy, especially before it is viable; the fatal expulsion of a foetus from the womb before term. [from 17th c.] Synonym: spontaneous abortion https://en.wikipedia.org/wiki/Miscarriage

Usage notes

• The death of an infant during labour or after it has become viable is generally called a stillbirth.