Evaluation of fetal lung maturity in diamniotic twins

OBJECTIVE: This study was undertaken to evaluate the correspondence in feta l lung development between diamniotic twins. STUDY DESIGN: Lecithin/sphingomyelin ratios were determined for amniotic fl uid specimens collected from each sac in 58 diamniotic twin pregnancies. RESULTS: Overall, the lecithin/sphingomyelin ratios of twin A and twin B an d those of the larger and smaller twins of each pair were closely correlate d (r greater than or equal to 0.83, P <.001). When stratified by gestationa l age, however, the percentage disparity in lecithin/sphingomyelin ratios b etween members of twin pairs was significantly greater at less than or equa l to 32 weeks' gestation (25%) than at >32 weeks' gestation (15%, P =.027). An analysis of the lecithin/sphingomyelin ratios of twins with a large lec ithin/sphingomyelin ratio disparity (greater than or equal to 20%) suggeste d that this disparity was a result of 1 twin having a lecithin/sphingomyeli n ratio that was advanced for gestational age with respect to that of the c o-twin. Disparities in lecithin/sphingomyelin ratio were not significantly affected by fetal sex or by discordance in size between the twins. CONCLUSION: At relatively early stages of diamniotic twin gestation (less t han or equal to 32 weeks' gestation), lecithin/sphingomyelin ratios should be obtained for both amniotic sacs to ensure accurate assessment of fetal l ung maturity in both twins.