Contemporary uses of "lethal" or "life limiting" terminology in perinatal research

A life-limiting fetal diagnosis (LLD) refers to a medical condition identified during pregnancy that is expected to lead to stillbirth, preclude ex utero survival, or significantly reduce neonatal life expectancy. The terms 'lethal' or 'life-limiting' are used to prognosticate early death for various anatomic or physiologic causes, although the expected timeframe is nonspecific. The purpose of this manuscript is to review how the terms 'lethal' or 'life limiting' are used in contemporary perinatal research.

Depending on the study design, 'life-limiting' is defined either prior to data analysis (such as prospective cohort studies), or after outcomes are assessed (such as case series). When 'life-limiting' is defined prior to data analysis, study-specific specific definitions may include timeframes from birth to death, probability of neonatal mortality, or a list of diagnoses based off billing codes.

Professional societies have guidelines to standardize the reporting of vital statistics, including early death. While these fall short of defining LLDs comprehensively, they present an opportunity for more specific prognostication following prenatal diagnosis, which may improve research standardization to facilitate a clearer understanding of LLDs in clinical practice.