Oral poster abstracts in utero in almost a third of fetuses and can be occasionally complete in some. OP02.35 Renal tubular dysgenesis: an unusual but potentially diagnosable cause of second-trimester oligohydramnios Objective: Renal tubular dysgenesis (RTD) is a lethal, irreversible renal abnormality presenting as severe oligohydramnios in mid second trimester. Cases can have autosomal recessive inheritance or are acquired. We describe prenatal findings in 3 cases detected by us and review the literature for diagnostic features. Methods: IRB approved review of records for histologically proven RTD cases. Literature review. Results: We managed three fetuses with proven RTD: 2 sibs and 1 sporadic. Pregnancies were otherwise unremarkable. All were singleton. There was no history of hypoxia or teratogen exposure including angiotensin converting enzyme (ACE) inhibitors. All had normal ultrasound examinations at 17-25 weeks but developed severe second-trimester oligohydramnios (23-26 wks). At onset, kidneys appeared normal or showed slight echogenic enlargement. All had cranial bone hypoplasia and wide sutures (hypocalvaria) confirmed by postnatal X-ray. One had echogenic bowel confirmed on X-ray and autopsy. Literature review revealed about 60 similar cases since 1983. Oligohydramnios was detected at 19 to 34 wk gestation. Hypocalvaria was recognized whenever sought. Most had findings of Potter sequence. Additional features included: previously affected sib, hypoxic and twinning complications and maternal hypertension treated with ACE inhibitors. All liveborns had profound renal failure and died at or shortly after birth. Histologically, the kidneys show characteristic absence of proximal convoluted tubules. Conclusions: Lethal fetal RTD may be suspected in fetuses with second-trimester onset of unexplained severe oligohydramnios who show normal size kidneys and hypocalvaria. Supporting features include history of an affected sib, and conditions which decrease renal blood flow such as fetal hypoxia, twinning complications, or maternal ACE inhibitor exposure. The recent delineation of associated genes may enable early prenatal diagnosis in at risk couples.