Ultrasound-Guided Intrauterine Labeling of Rat Fetuses.

<bold>Aim: </bold>To compare intra-amniotic versus fetal subcutaneous injections for selective fetal labeling in multifetal rat pregnancies.<bold>Methods: </bold>A total of 14 pregnant rats were randomized to receive intra-amniotic injections of dyes (including Fluorescein, Indigo Carmine, or Evans Blue) or fetal subcutaneous injections (of commercial tattoo ink) both guided by ultrasound at 15-17 days of gestation. Survival, injection, and labeling success rates of both techniques were compared.<bold>Results: </bold>Survival rates (84.4% for intra-amniotic injections vs. 90.9% for fetal subcutaneous injections) and injection success rates (94% for intra-amniotic injections vs. 100% for fetal subcutaneous injections) were similar among both groups. None of the neonates from the intra-amniotic injections group were labeled at birth, while 93% of the neonates from fetal subcutaneous injections group were tagged, showing a visible spot in the skin at birth.<bold>Conclusion: </bold>Our results suggest that ultrasound-guided fetal subcutaneous injections might be an adequate strategy for selectively labeling fetuses in multifetal pregnant animals. [ABSTRACT FROM AUTHOR]