Diagnosis & Testing

Following a Polyhydramnios diagnosis, routine testing should include a GTT, NSTs, BPPs, and growth scans, with additional testing in more severe cases.

Table of Contents

Diagnosis

Polyhydramnios is a secondary diagnosis; it is a condition that happens as a result of something else. Diagnosing Polyhydramnios is the easy part, finding the primary condition that is causing it may prove to be more difficult. In fact, in 60% of cases, the cause does not get identified before birth.

If your healthcare provider suspects you might have Polyhydramnios, he/she will order an ultrasound of your baby to measure the amniotic fluid level. If your total amniotic fluid index is greater than 24 cm or you have a single deepest pocket greater than 8 cm then you will probably be diagnosed with Polyhydramnios

After receiving the diagnosis it is important to talk to your provider about the follow-up tests that you will need. 

Determining an accurate cause of your Polyhydramnios can help both you and your provider prepare for what is to come. But keep in mind that not all things that cause Polyhydramnios can be detected prenatally.

Standard Tests:

Oral glucose tolerance test

Non-stress test

Biophysical profile

Growth scan

Additional Tests:

Fetal echocardiogram

 Maternal blood grouping 

Rhesus factor antibody screening

Maternal ToRCH screening

Middle cerebral artery peak systolic velocity ultrasound

Karyotyping/Microarray

Whole exome sequencing

Standard Tests

These tests should always be ordered following a diagnosis of Polyhydramnios.

Glucose Tolerance Test

An Oral Glucose Tolerance Test is a routine test done around 28 weeks that checks for gestational diabetes. If you’ve already had the test done and passed, your provider will likely have you take it again to rule out the late onset of diabetes.

There are two types of glucose tolerance tests, a one-hour test or a three-hour test. In both tests, you drink a special glucose mixture and then have your blood drawn to see how your body processes the sugar. If you are repeating the test, your provider may opt to skip the one-hour test and go straight to the three-hour test since it is considered more reliable.

NST

A Non-Stress Test (NST)  is a non-invasive procedure that checks how your baby’s heart reacts to his/her movement. It also measures the strength of any contractions you are having.

During the procedure, you have two monitors placed on the outside of your belly and hooked up to a screen. One monitor measures the presence or absence of contractions during the test. The other monitor is placed over your baby’s heart to keep track of his/her heart rate for approximately 20-30 minutes.

Typically, any time your baby moves, his/her heart rate briefly increases and then comes back down to its baseline. Your provider is looking for two of these accelerations during the test. This test can help your provider determine if your baby is in distress from low oxygen levels.

BPP

A Biophysical Profile (BPP) is another non-invasive test that combines the NST with an ultrasound to check your baby’s breathing, muscle tone, and movement, as well as your amniotic fluid level. Each portion of this test is given a score from 0-2.

A low score on a BPP indicates a need for a repeat BPP, further testing, or possible intervention. A BPP can sometimes detect genetic anomalies or other problems your baby may experience, and it will help your provider determine if any additional testing may be needed.

Growth Scan

A Growth Scan is a simple ultrasound procedure done to measure the growth of your baby. This scan is sometimes done along with a BPP. It usually measures your baby’s head, waist, and thigh bone, and may give you an estimate of your baby’s weight.

A growth scan is useful in detecting very large (macrosomia) or very small (IUGR) babies. Large babies may need to be evaluated for overgrowth syndromes if diabetes has been ruled out. IUGR in Polyhydramnios has been linked to very poor outcomes for the baby, so identifying a very small baby is critical to his/her further evaluation and management.

Additional Screening Tests

Some of these tests may be ordered as part of a routine workup for Polyhydramnios, others may only be ordered if there are additional concerns.

Fetal Echo

A Fetal Echocardiogram is a high-resolution ultrasound that specifically checks your baby’s heart structure and function. This ultrasound is performed by a specially trained sonographer and interpreted by a perinatal cardiologist. It usually takes 45-120 minutes, depending on the findings.

A fetal echocardiogram should be ordered when there is reason to suspect fetal heart problems. 

SEVERE IDIOPATHIC POLYHYDRAMNIOS SHOULD BE CONSIDERED AS A REASON TO INVESTIGATE FOR HEART CONDITIONS. 

Other possible risk factors for fetal heart problems include a family history of CHD, heart defects or arrhythmias on routine ultrasound, a chromosomal or genetic anomaly, extra fluid surrounding fetal organs, maternal infections, or abnormalities of fetal organs. A fetal echocardiogram is useful to help determine if pre-delivery planning or postnatal medical management will be needed to care for special heart abnormalities in your baby.

Maternal Blood Grouping & Rhesus Factor Antibody Screening

Maternal blood grouping and rhesus factor antibody screening are used to determine if preventative measures or further evaluation for fetal anemia is needed. Maternal blood grouping and RH factor screening is usually done as part of routine blood work during your first prenatal visit to find out if you have a positive or negative RH-factor. If you are RH positive, no further testing is needed.

If you are found to have a negative RH factor then you will also need to have the RH factor antibody screening test done to see if your body is producing RH positive antibodies (antibodies that attack RH positive blood). This test is usually done in the first trimester, again at 28 weeks, and again after delivery if your baby has RH-positive blood. If you are newly diagnosed with Polyhydramnios and it has been more than one month since your last antibody screen, it needs to be repeated.  

If your antibody screen shows you are not producing Rh-positive antibodies, then you will receive RhoGAM to help keep your body from producing the antibodies. If your antibody screening test shows that you are producing Rh-positive antibodies, RhoGAM won’t help, and your baby will need to be closely monitored for signs of fetal anemia. 

Maternal ToRCH Screening

Maternal ToRCH Screening is a simple blood test used to check for a specific group of infections known to cause problems for babies. ToRCH stands for toxoplasmosis, other (syphilis, HIV, varicella, mumps, parvovirus), rubella, cytomegalovirus, and herpes simplex. Your healthcare provider may do a partial ToRCH test as part of your routine blood work in early pregnancy.

Later, if you show signs of infection or if your provider sees signs of a possible infection in your baby on an NST or BPP, they will likely order a full ToRCH workup. Depending on your test results, you may need additional screening tests so that your baby can receive the best care both prenatally and after delivery.

MCA Peak Systolic Velocity Ultrasound

A Middle cerebral artery (MCA) peak systolic velocity is a very specific non-invasive ultrasound measurement that is used to check for fetal anemia. MCA peak systolic velocity is measured by a specially trained sonographer or perinatologist.

This technique is becoming more widely used to replace more invasive techniques such as amniocentesis in cases where your baby is at risk for fetal anemia. While it does not predict every case of fetal anemia, the technique is proving to be highly accurate especially among providers proficient in it. If your provider believes your baby may be at risk for fetal anemia, this specialized ultrasound measurement should be considered. 

Karyotyping & Microarray

Karyotyping and Microarray are genetic tests that look for extra, missing, or abnormal pieces of chromosomes. These two tests are similar except that microarray is designed to detect much smaller changes in the chromosomes than karyotype.

These tests are the standard first-line tests used when a genetic anomaly is present on ultrasound. They can be useful in determining if your baby has a change in their chromosomes that can cause many different genetic syndromes. However, these tests are far from perfect and must be done only after thorough genetic counseling and understanding of the complexity of the results.

Whole Exome Sequencing

Whole exome sequencing (WES) is a relatively newer genetic test that can detect changes in the exomes of your baby’s DNA. The exome makes up only around 1% of your DNA, but it contains the protein parts where a huge majority of genetic diseases/disorders are linked. Because WES looks at your individual genetic material and not just whole chromosomes, it can detect many things that karyotyping and microarray cannot.

(Think of it like this: Pretend genetic testing is being used to look for spelling errors in a document. We’re looking for errors in the word, “there”. Karyotype and microarray can pick up extra letters, “thhere”, missing letters, “tere”, or changes to letters, “tlere”. WES, though, can pick up an entirely different kind of change like “their” or “they’re”.

WES is an innovative and powerful tool that can discover a genetic anomaly early on so that a proper plan of treatment can be established. But, like other genetic tests, it is far from perfect and the results can be very complex to understand, even frustrating if they are too vague.

WES is usually only approved when there is evidence of a genetic anomaly on ultrasound, and after karyotyping/microarray has been done. However, severe polyhydramnios in the absense of diabetes or other known causes may be enough reason to have this testing approved. Additionally, if your baby also experiences any complications after delivery it may help expedite the process of approval for WES.

If you would like to pursue this option, we suggest you read up on whole-exome sequencing and speak to your MFM about having it done. (Click this link to read about the applications of WES in prenatal genetics.) Genetic counseling from a geneticist trained in interpreting these complex results is a must before this test should be considered. 

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Treatment & Monitoring – Treatment for Polyhydramnios includes management of the underlying condition (when possible), fetal surveillance, reducing fluid, and creating an effective care plan. 

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