What is urinary tract dilation?

Urinary tract dilation occurs when part of the unborn baby’s urinary tract swells (dilates) abnormally with excessive amounts of urine. The swelling is often caused by a blockage or narrowing of the urinary tract, which stops or slows the urine from leaving the baby’s body. Usually, the swelling goes away on its own, either during the pregnancy or after the baby is born. In more severe cases, which are uncommon, the condition can lead to low levels of amniotic fluid (oligohydramnios).

The urinary tract consists of two kidneys, two ureters, a bladder, and a urethra. Special arteries in the kidneys make the urine, which then drains into a funnel-shaped area near the opening of each kidney known as the renal pelvis. From there the urine travels via the ureters to the bladder, which collects the liquid before it exits the body through the urethra. When urine leaves an unborn baby, it becomes the main part of the amniotic fluid, the protective liquid that surrounds the baby in the womb. The amniotic fluid plays an essential role in the baby’s development, particularly lung development.

In most cases of urinary tract dilation, the abnormal buildup of urine occurs in the renal pelvis. But the urine can get blocked further down the urinary tract as well, causing the ureters, bladder, or urethra to swell. (Figure).

Urinary Tract Dilation image

Figure – Urinary tract dilation occurs when a normal urinary tract (left) becomes swollen, or dilated, with fluid (right).

Who will be on my care team?

At Midwest Fetal Care Center, a collaboration between Children’s Minnesota and Allina Health, we specialize in individual attention that starts with you having your own personal care coordinator to help you navigate your baby’s treatment process. We use a comprehensive team approach to urinary tract dilation and any associated conditions. That way, you are assured of getting the best possible information by some of the most experienced physicians in the country. For urinary tract dilation, your care team will include a maternal-fetal specialist, a pediatric urologist, a neonatologist, a geneticist, a nurse specialist care coordinator, and several other technical specialists. This entire team will follow you and your baby closely through the evaluation process, and will be responsible for designing and carrying out your complete care plan.

Meet the team

What causes urinary tract dilation?

As with most birth defects, the cause of urinary tract dilation is unknown. The condition appears to run in some families, so it’s not unusual for a parent, sibling, or cousin to have had urinary tract dilation or some other kidney issue in childhood. In rare instances, urinary track dilation is due to a genetic or chromosomal condition, such as Down syndrome (trisomy 21). Most cases of urinary tract dilation develop in otherwise healthy babies, however.

How is urinary tract dilation diagnosed?

Urinary tract dilation is diagnosed by ultrasound. In most cases, mild dilation (swelling) of the kidney is seen on the ultrasound routinely done at the 20th week of pregnancy. Because kidney dilation seen at 20 weeks often completely resolves later in pregnancy, your doctor or midwife will send you for a follow-up ultrasound at 32-36 weeks to reassess the kidneys, bladder, and urinary tract. If dilation of the kidneys or of other areas of the urinary tract is still present at 32-36 weeks, your baby will be diagnosed with urinary tract dilation.

What are the different classifications of urinary tract dilation?

Most unborn babies have a low-risk type of urinary tract dilation known as UTD A1. In these instances, only the renal pelvis is dilated, and the dilation is moderate (7 to 10 millimeters after the 28th week of pregnancy). UTD A1 often resolves spontaneously during pregnancy.

If the dilation of the renal pelvis is more severe (greater than 10 millimeters), or if there are other abnormalities of the urinary tract (a dilated ureter or urethra, an abnormal bladder, or abnormal-appearing kidney tissue) then the baby has a higher-risk type of urinary tract dilation known as UTD A2-3.

How is urinary tract dilation managed before birth?

Urinary tract dilation is not treated before birth if the amniotic fluid level remains normal. After the condition is diagnosed, however — usually as a result of the ultrasound done routinely at the 20th week of pregnancy — we may continue to monitor your baby with high-resolution fetal ultrasonography at intervals throughout the pregnancy.

What is high-resolution fetal ultrasonography?

High-resolution fetal ultrasonography is a non-invasive test performed by one of our ultrasound specialists. The test uses reflected sound waves to create images of your baby within the womb. We will use ultrasonography to follow the development of your baby’s urinary tract and other internal organs, as well as his or her overall growth. We will also use it to measure the volume of amniotic fluid that surrounds the baby throughout the pregnancy.

What happens after my evaluation is complete?

After we have gathered all the anatomic and diagnostic information about your baby, our maternal-fetal specialist will meet with you to discuss the results and share our recommendations. We will connect you to a nurse specialist care coordinator who will assist with setting up future consultations and follow-up care for the baby after birth. One of those consultations will be with a pediatric urologist, who will meet with you either during the pregnancy or soon after the baby is born. We will also communicate with your primary obstetrician or midwife so that he or she can continue to provide your routine prenatal care.

How is urinary tract dilation treated after birth?

Urinary tract dilation does not change when or how you deliver. Your baby will not need to be delivered early. Nor will your baby need to be delivered by cesarean section, although, like all women, you may need early delivery or a C-section for other obstetric reasons. It is also very likely that you will be able to deliver your baby with your primary obstetrician or midwife at your local hospital.

If your baby has very dilated kidneys, however, or has low amounts of amniotic fluid (oligohydramnios), he or she may need specialized medical care after birth in a newborn intensive care unit (NICU).  In such a case, we recommend your baby be born at The Mother Baby Center at Abbott Northwestern and Children’s Minnesota in Minneapolis or at The Mother Baby Center at United and Children’s Minnesota in St. Paul. Children’s Minnesota is one of only a few centers nationwide with a birth center located within the hospital complex. This means that your baby will be born just a few feet down the hall from our NICU.

We will assist you with scheduling a visit with a pediatric urologist during the first few weeks of your baby’s life. At that time, your baby will have an ultrasound of his or her kidneys and bladder — and possibly other testing — to see if the baby will need any post-birth treatment.

Will my baby need an operation?

In many cases, no treatment is needed, as the condition resolves on its own without any long-lasting medical problems. An antibiotic is sometimes prescribed, however, to prevent a urinary tract infection.

If your baby has advanced urinary tract dilation (UTD A2-3), surgery may be needed to correct the underlying structural problem that is blocking the normal flow of urine. To prevent lasting kidney damage, the surgery is usually done before the child’s second birthday.

What is my baby’s prognosis?

Most babies with urinary tract dilation have an excellent prognosis. Usually, the urinary tract dilation resolves on its own completely after birth. In cases where the condition is due to a structural blockage, surgery can often fix the problem.

Will my baby require long-term follow-up?

The findings from your baby’s ultrasound taken after birth will determine whether or not follow-up care with a pediatric urologist is needed. Such care, which may include surgery, can decrease the risk of kidney problems for your baby later in life. The pediatric urologist will recommend an individualized management plan for your baby based on your baby’s specific ultrasound findings.

Contact us

Need a referral or more information? You or your provider can reach the Midwest Fetal Care Center at 855-693-3825.