urinary tract consists of
- two kidneys, which filter waste materials and excess water from the blood
- two ureters, which carry urine from the kidneys to the bladder
- the bladder, where urine is stored until it is released
- the urethra, where urine flows out
of the body
Normal urinary tract
We rely on our kidneys and urinary system to keep fluids and natural
chemicals in our bodies balanced. While a baby is developing in the mother’s
womb, much of that balancing is handled by the mother’s placenta. The baby’s
kidneys begin to produce urine at about 10 to 12 weeks after conception, but the
mother’s placenta continues to do most of the work until the last few weeks of
the pregnancy. Wastes and excess fluid are removed from the baby’s body through
the umbilical cord. The baby’s urine is released into the amniotic sac and
becomes part of the amniotic fluid. This fluid plays a role in the baby’s lung
Sometimes, a birth defect in the urinary tract will block the flow of urine
in an unborn baby. As a result, urine backs up and causes the ureters and
kidneys to swell. Swelling in the kidneys is called hydronephrosis. Swelling in
the ureters is called hydroureter.
Swelling in the kidney is called hydronephrosis. Swelling in the ureter is called hydroureter.
Hydronephrosis is the most common problem found during ultrasound examination
of babies in the womb. The swelling may be barely detectable or very noticeable.
The results of hydronephrosis may be mild or severe, but the long-term outcome
for the child’s health cannot always be judged by the severity of swelling.
Urine blockage may damage the developing kidneys and reduce their ability to
filter. The blockage may also raise the risk that the child will develop a
urinary tract infection (UTI). Recurring UTIs can lead to more permanent kidney
damage. In the most severe cases of urine blockage, the amniotic sac is so
reduced that the lack of fluid threatens the baby’s lung development.
Types of Defects in the Urinary Tract
Hydronephrosis can result from many
types of defects in the urinary tract. Doctors use specific terms to describe
the type and location of the blockage.
- Vesicoureteral reflux (VUR). The openings where the ureters empty urine into
the bladder should work like valves to keep urine from backing up into the
ureters. Sometimes the valve doesn’t work properly and urine flows back into the
kidneys. The urine may flow only a short way back into the ureters, or it may go
all the way back to the kidneys, causing the ureters and kidneys to swell. VUR
may occur in only one ureter or in both. Kidneys with severe reflux may not
develop normally, and after birth kidneys with reflux may be at risk for damage
Ureteropelvic junction (UPJ) is the point where the ureter joins the kidney.
- Ureteropelvic junction (UPJ) obstruction. The point where the ureter joins
the kidney is called the ureteropelvic junction. If urine is blocked here, only
the kidney swells. The ureter remains at a normal size. UPJ obstruction usually
only occurs in one kidney.
- Bladder outlet obstruction (BOO). BOO describes any blockage in the urethra
or at the opening of the bladder. The obstruction may occur in boys or girls.
The most common form of BOO seen in newborns and during prenatal ultrasound
examinations is posterior urethral valves (PUV). BOO caused by PUV occurs only
- Posterior urethral valves (PUV). In boys, sometimes an abnormal fold of
tissue in the urethra keeps urine from flowing freely out of the bladder. This
defect may cause swelling in the entire urinary tract, including the urethra,
bladder, ureters, and kidneys.
- Ureterocele. If the end of the ureter does not develop normally, it can
bulge, creating what is called a ureterocele. The ureterocele may obstruct part
of the kidney or the bladder.
Ureterocele. The inset shows a cross-section of the ureter bulging into the
interior of the bladder.
- Nerve disease. Urination requires coordinated nerve signals between the
bladder, spinal cord, and brain. Spina bifida and other birth defects that
affect the spinal cord may interrupt nerve signals and lead to urine retention
Syndromes That May Affect the Urinary Tract
In addition to defects that occur
in a single spot in the urinary tract, some babies are born with genetic
conditions that affect several different systems in the body. A condition that
includes multiple, seemingly unrelated problems, is called a syndrome.
- Prune belly syndrome (PBS). Occurring only in boys, PBS causes a baby to
have an enlarged abdomen because the normal abdominal wall muscles are missing
or very weak. The entire urinary tract is enlarged, and both testicles remain
inside the body instead of descending into the scrotum. The skin over the
abdomen is wrinkled, giving the appearance of a prune. Most children with PBS
have hydronephrosis and VUR.
- Esophageal atresia (EA). EA is a birth defect in which the esophagus is
incomplete. The esophagus is the tube that carries food from the mouth to the
stomach. About 30 percent of babies born with EA will have problems in other
body systems, such as the heart or urinary tract.
- Congenital heart defects. Heart defects range from mild to life threatening.
Children born with heart defects also have a higher rate of problems in the
urinary tract than children in the general population, suggesting that some
types of heart and urinary defects may have a common genetic cause.
Birth defects and other problems of the urinary tract may be
discovered before the baby is born, at the time of birth, or later, when the
child is brought to the doctor for a urinary tract infection or urination
Tests during pregnancy can help determine if the baby is
developing normally in the womb.
- Ultrasound. Ultrasound uses sound waves to produce a picture on a television
screen. A wand gliding on the mother’s abdomen directs harmless sound waves into
the womb. The sound waves bounce off the baby and back into the wand to create a
black-and-white image on the screen. Ultrasound images can even display internal
organs within the baby, so enlarged kidneys, ureters, or bladder may be visible.
- Amniocentesis. In amniocentesis, the doctor inserts a needle through the
mother’s skin into the amniotic sac to collect about an ounce of amniotic fluid.
The fluid contains genetic material from the baby that can be analyzed for signs
- Chorionic villus sampling (CVS). In CVS, the doctor collects a small piece
of tissue from the placenta using a needle passed through the mother’s vagina
and cervix. The placenta has the same genetic makeup as the baby.
Most healthy women do not need all the tests. Ultrasound examinations during
pregnancy are routine, although they are not always required and rarely
influence treatment decisions. Amniocentesis and CVS are recommended only when a
risk of genetic problems exists because of family history or something detected
during an ultrasound. Amniocentesis and CVS carry a slight risk of harming the
baby and mother, or ending the pregnancy in miscarriage, so those risks should
be weighed carefully against the potential benefits of learning about the baby’s
Ultrasound allows evaluation of a baby’s internal organs, even before birth.
Examination of Newborn
Sometimes a newborn does not urinate as
expected, even though prenatal testing showed no sign of urine blockage. The
baby may urinate only small amounts or not at all. An enlarged kidney may be
felt during the newborn examination as well. Different imaging techniques are
available to determine the cause of the problem.
- Ultrasound. Once the baby is born, ultrasound can be used to view the baby’s
urinary tract directly for a clearer image than could be achieved while the baby
was in the womb.
- Voiding cystourethrogram (VCUG). If the doctor suspects that urine is
backing up into the ureters or that the bladder outlet is obstructed, a VCUG may
be needed. In this test, a catheter is used to fill the child’s bladder with
warm liquid containing iodine to make it visible on an x ray. A video records
the x-ray images of the bladder as it is filled and as the child urinates. The
video will reveal reflux if the liquid enters the ureters and blockage of the
bladder in the case of an obstruction, such as PUV.
- Nuclear scan. A nuclear scan involves injecting a very small amount of
radioactive material, just enough to show up using a camera that captures gamma
rays. The amount of radioactive substance used is determined by the child’s
weight. The liquid is injected into the child’s bloodstream and eventually
passes through the kidneys, where it is filtered from the blood and directed
down the ureters to the bladder. The camera may be mounted above or below a
table where the patient lies. The camera passes over or under the urinary tract
as the child lies on the table.
Sometimes urine blockage is not
apparent until the child develops the symptoms of a urinary tract infection.
These symptoms include
If these symptoms persist, the child should be seen by a doctor. For any
fever in the first 2 months of life, the child should be seen by a doctor
immediately. The doctor will ask for a urine sample to test for bacteria. The
doctor may also recommend imaging tests including ultrasound, VCUG, or nuclear
Treatment for urine blockage depends on the cause and severity of
the blockage. Hydronephrosis discovered before the baby is born will rarely
require immediate action, especially if it is only on one side. Often the
condition goes away without any treatment before birth or sometimes after. The
doctor will keep track of the condition with frequent ultrasounds. With few
exceptions, treatment can wait until the baby is born.
If the urine blockage threatens the life of the unborn baby,
the doctor may recommend a procedure to insert a small tube, called a shunt,
into the baby’s bladder to release urine into the amniotic sac. The placement of
the shunt is similar to an amniocentesis, in that a needle is inserted through
the mother’s abdomen. Ultrasound guides the placing of the shunt. This fetal
surgery carries many risks, so it is performed only in special circumstances,
such as when the amniotic fluid is absent and the baby’s lungs aren’t developing
or when the kidneys are very severely damaged.
Antibiotics are medicines that kill bacteria. A newborn with
possible urine blockage or VUR may be given antibiotics to prevent urinary tract
infections from developing until the urinary defect corrects itself or is
If the urinary defect doesn’t correct itself and the child continues
to have urine blockage, surgery may be needed. The decision to operate depends
upon the degree of blockage. The surgeon will remove the obstruction to restore
urine flow. A small tube, called a stent, may be placed in the ureter or urethra
to keep it open temporarily while healing occurs.
If the child has urine retention because of
nerve disease, the condition may be treated with intermittent catheterization.
The parent, and later the child, will be taught to drain the bladder by
inserting a thin tube, called a catheter, through the urethra to the bladder.
Emptying the bladder in this way helps prevent kidney damage, overflow
incontinence, and urinary tract infections.
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Hope Through Research
Researchers from universities and government
agencies are working to understand the causes of urinary birth defects and to
find more effective treatments. Through its Pediatric Urology Program, the
National Institute of Diabetes and Digestive and Kidney Diseases funds research
into bladder and urinary tract development, prenatal interventions for urinary
tract disorders, and bladder abnormalities associated with spina bifida.
Additionally, the Eunice Kennedy Shriver National Institute of Child Health and
Human Development has established the Birth Defects Initiative to study the
genetic and molecular mechanisms underlying developmental processes of the
For More Information
Eunice Kennedy Shriver National Institute of Child Health and Human
Information Resource Center
P.O. Box 3006
Rockville, MD 20847
Email: [email protected]