Blind versus ultrasound guided intra-amniotic injection in the rabbit model of congenital diaphragmatic hernia Eastwood MP, Jimenez J, Richter J, Nagomato T, Zia S, Toelen J, Deprest JA KU Leuven, Leuven, Belgium Objective Intra-amniotic (ia) delivery of active components allows pulmonary uptake by natural fetal breathing. Human CDH fetuses, similar to experimental animals, such as rabbit pups with diaphragmatic hernia (DH) have been shown to “inhale” active compounds. The present study compares intra-amniotic injection in fetal rabbits with or without a previously created diaphragmatic hernia to determine if ultrasound (us) guided injection is superior to blind ia injection. Methods Six New Zealand white rabbits had DH creation in 17 fetuses on gestational day (gd) 23 (term=31). On gd 26 fetuses were assigned randomly to ia injection of 1ml of chinese ink (ci) either blind or under us guidance (Vevo Visualsonics, Toronto, Canada) under the chin by a single operator (mpe). The presence of amniotic fluid as visible under ultrasound was noted (deepest vertical pool (dvp) in mm). Unoperated littermates of injected and non-injected pups, served respectively as positive or negative controls (table 1). Fetuses were harvested 48 hours late. The presence of ci in the amniotic sac and/or fetus was confirmed at harvest and on histology by two independent observers blinded to the treatment group. Lung to body weight was documented. Results Survival rate following injection was very high, similar in CDH and non-CDH fetuses. Ci was identified in injected lungs on histology in all but one injected case, this fetus on harvest however had a confirmed intra-amniotic injection. Intra-fetal injection, usually in the soft tissues of the neck or head did not preclude inhalation. DVP was immeasurable in all but one CDH fetus precluding ultrasound guided injection. Average DVP was 6. 6mm (3. 1-8. 9) in control fetuses. Injection of ci had no effect on fetal lung to body weight ratio (LBWR) (p=04124). Conclusion Following intra-amniotic injection ci particles could always be traced into the fetal lung or confirmed as an intra-amniotic injection at harvest visually. Accidental fetal neck injection only occurred in the blind injections group (30%). Following induction of CDH there is virtual anhydramnios on ultrasound therefore us guided injection is not possible.