Performance of lecithin-sphingomyelin ratio as a reflex test for documenting fetal lung maturity in late preterm and term fetuses.

Objective: To determine if infants delivered after immature or indeterminate TDx-FLM II testing and a mature reflex test are at increased risk for neonatal respiratory complications.

Methods: The primary analysis compared neonatal respiratory morbidity (RDS or TTN) in 34-39-week fetuses delivered after either (i) mature TDx-FLM II testing, or (ii) indeterminate or immature TDx-FLM II and a positive reflex test (PG or L/S ratio).

Results: Fifty patients delivered after mature TDx-FLM II, and 30 after immature or indeterminate TDx-FLM II with an L/S ≥ 2.0. Respiratory morbidity was significantly higher in the group delivered after mature reflex testing compared with mature TDx-FLM II (23% vs. 2%, p < 0.01). When PG was present, there were no cases of RDS or TTN.

Conclusions: Utilizing L/S ratios as a reflex test to confirm lung maturity was associated with a high risk for respiratory morbidity, particularly when PG was not present.