Bilateral renal agenesis, a condition where a baby develops without either kidney, was considered universally fatal until very recently. Without intervention, babies born with this condition die within hours or days because their lungs never developed enough to breathe. But a groundbreaking fetal therapy has changed the picture: in the first major clinical trial, 35% of babies born alive after treatment survived to go home from the hospital on long-term dialysis.
That number represents real progress from a zero percent survival baseline, but it also means the majority of treated babies still do not survive. Understanding why, and what the path looks like for those who do, requires knowing what bilateral renal agenesis actually does to a developing baby.
Why Missing Kidneys Affects the Lungs
The kidneys themselves aren’t what kills these babies. The fatal problem is what happens to the lungs when no kidneys are present. Starting in the second trimester, fetal urine becomes the primary source of amniotic fluid. A baby without kidneys produces no urine, so amniotic fluid drops to dangerously low levels or disappears entirely.
Amniotic fluid does two critical things for lung development. First, it gives the baby physical space to move and expand its chest. Without enough fluid, the walls of the uterus compress the baby’s body, collapsing the airways and preventing the lungs from growing. Second, amniotic fluid supplies proline, an amino acid the lungs need to develop properly. The result is severely underdeveloped lungs, a condition called pulmonary hypoplasia. At birth, these lungs simply cannot exchange enough oxygen to sustain life. This chain of events is known as Potter sequence.
How It’s Detected Before Birth
Bilateral renal agenesis is rare, occurring in roughly 3 out of every 100,000 births based on large surveillance data from over 25 million births in China. It’s typically spotted on a routine mid-pregnancy ultrasound when the sonographer can’t visualize either kidney and notices very low or absent amniotic fluid.
Several ultrasound markers help confirm the diagnosis. The adrenal glands, which normally sit on top of the kidneys and appear in an inverted Y or V shape, flatten into a straight line when no kidney is underneath them. Color Doppler imaging will show no renal arteries branching off the aorta, since there are no kidneys to supply with blood. A recently described marker is a segmental forward deviation of the aorta in the area where the renal arteries would normally connect. Together, these signs give doctors high confidence in the diagnosis before birth.
Serial Amnioinfusion: The Treatment That Changed Outcomes
The idea behind serial amnioinfusion therapy is straightforward: if the baby can’t make amniotic fluid, put it back in artificially. The technique was first attempted in the 1980s, but it took decades of refinement before it became a structured treatment option. The procedure involves inserting a needle through the mother’s abdomen into the uterus and infusing saline to restore fluid levels, repeated multiple times throughout the pregnancy.
In the Renal Anhydramnios Fetal Therapy (RAFT) trial, the first formal clinical trial of this approach, infusions typically began around 24 weeks of pregnancy and needed to start by 26 weeks at the latest. The median number of infusions per pregnancy was 9, though some mothers underwent as many as 26 procedures. Each session delivered roughly 300 to 800 milliliters of fluid. Some protocols use fewer, larger-volume infusions to reduce the cumulative risk of complications from repeated needle insertions, while others spread smaller amounts across more sessions.
The goal isn’t to fix the kidneys. It’s purely about buying the lungs enough time and space to develop to a point where the baby can breathe after delivery.
Survival Numbers From the RAFT Trial
The RAFT trial results, published in JAMA, provide the clearest picture of what’s currently possible. Of the pregnancies that received serial amnioinfusions, 17 babies were born alive. Of those 17, six survived to hospital discharge, a 35% survival rate among live births. All six went home on peritoneal dialysis. At the time the results were published, none had yet received a kidney transplant.
The median hospital stay before discharge was about 24 weeks, meaning these families spent roughly six months in the hospital after birth. For the 11 babies who did not survive beyond the first two weeks of life, the cause was the same problem the treatment aimed to prevent: lungs that hadn’t developed enough despite the infusions.
These numbers represent a specific, carefully selected group. To enter the trial, mothers had to begin infusions by 26 weeks, deliver at a specialized RAFT center, and commit to postnatal care including long-term dialysis at that same center. Results outside of trial conditions, where access to expertise and follow-up may vary, could look different.
What Life Looks Like After Birth
Surviving birth is only the first hurdle. A baby born without kidneys needs dialysis immediately and will need it continuously until a kidney transplant becomes possible. For newborns, peritoneal dialysis is the standard approach. It works by filling the abdominal cavity with a special fluid that draws waste products out of the blood, then draining and replacing it on a regular cycle.
Starting dialysis in a newborn is technically challenging. In preterm or small babies, catheter placement is difficult, especially if the infant is swollen or underweight. In one study of kidney replacement therapy in low-birth-weight newborns, dialysis was started at a median weight of about 1.85 kilograms (roughly 4 pounds) and at around 16 days of age. Most infants tolerated initiation without major drops in blood pressure, though the process requires close monitoring.
The long-term plan for every surviving baby is a kidney transplant. There are no absolute size or age cutoffs that disqualify a child, but smaller children (those under about 15 kilograms, or 33 pounds) face higher surgical risks and higher mortality rates while waiting on dialysis. Most transplant teams aim to perform the surgery as soon as the child is large and stable enough to handle it. That typically means months to years of dialysis at home before transplantation becomes feasible.
Without Treatment
Without fetal intervention, bilateral renal agenesis remains lethal. The lungs are too underdeveloped to support breathing, and most babies die within minutes to hours after delivery. Before the advent of serial amnioinfusion, the standard approach after diagnosis was either pregnancy termination or comfort care after birth. Many families still choose this path after counseling, and the Chinese surveillance data reflects this reality: the vast majority of bilateral renal agenesis cases resulted in termination rather than live birth.
For families who receive this diagnosis today, the critical question is timing. The window for starting amnioinfusions closes at around 26 weeks of pregnancy, and earlier referral to a center with experience in this procedure gives the best chance of qualifying for treatment. Even with treatment, families face a long and uncertain road: a one-in-three chance of surviving to discharge, months in the hospital, years of dialysis, and an eventual transplant with its own lifelong demands. But for the first time, that road exists at all.