Prenatal Monitoring

Congratulations on your baby! All life is special and deserves to be celebrated. Antibodies can be a scary thing, but with a little help, everyone can understand them. Understanding your disease is so important to helping get your baby here safely. This page will provide an explanation of the tests that are required during an alloimmunized pregnancy. With proper testing/monitoring, and a skilled medical team, you have every chance at a great outcome. Write down any questions that you have for your care team in your notebook. Remember to discuss all tests and their results with your health care team. To make tracking your results easier, you can download and print a copy of the personal care record.

Blood Tests

Antibody Screen with Reflex to Titer

The blood test for mom that determines how many antibodies are in her system.

All pregnant women have an antibody screen run as part of their initial prenatal lab work. If this screen comes back positive, the lab will analyze the blood further to determine how many antibodies are in your blood. There are a few antibodies for which the antibody screen may come back negative, but the baby still be affected. These are anti-Dia, anti-Dib, anti-Jsa, and anti-Wra.

Titers are a measure of expressing the concentration of antibodies in your blood. In a first affected pregnancy, titers are drawn every 4 weeks until 28 weeks, then every 2 weeks until 36 weeks. After 36 weeks, they are drawn weekly until delivery at 37-38 weeks. If you have had a previously affected pregnancy or if you have anti-K antibodies, medical literature says that titers are not an effective monitoring tool. In subsequent pregnancies, titers are usually only drawn at the beginning of the pregnancy to determine if a woman is a candidate for early intervention and scans.

Your titers will come as a ratio. Such as 1:less than 1, 1:2, 1:4, 1:8, 1:16, 1:32, 1:1024, etc. This tells how many times the lab needed to dilute your blood to get rid of the antibodies. Every antibody has a “critical titer” level – this is the level at which there is significant risk for HDFN and weekly MCA scans should begin. The critical titer for all antibodies except anti-K is 1:16. The critical titer for anti-K is 1:4, though severe fetal anemia requiring intrauterine transfusions has occurred with titers as low as 1:2.

You should have additional MCA Doppler scans whenever you hit critical titer (1:16 for most antibodies, 1:4 for Kell), have a rise in titers, or have had a previously affected pregnancy.

What else should I know?
Titers can go up and down at random. Just because they are low now doesn’t mean they’ll stay low. Just because they are high, doesn’t mean they’ll get higher. Even having a cold can cause your titers to increase. 

Titers do not determine how baby will do after birth. Even moms with low titers, such as 1:2, can have babies at risk for brain damage from high bilirubin. Always get baby tested after birth, regardless of titer levels.

In the US they have now recommended that the 1: be dropped from the titer. So instead of saying 1:16, some places will just say a titer of 16. This is important because Quants (used in the UK and other places) are also shown as a number, but quants can include a decimal. Titers will never include a decimal, and will always be a 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, or 2048. Some places still report titers in the old way of 1:16, so we will continue to show them that way while also making a note about the decision to drop the 1: from the score.

To the left are titer tubes. In order to get the titer, each sample is taken and diluted by half. The last dilution that antibodies were detected in is the “titer”. For instance, my antibodies were originally detected in the tube 1:1, but not when diluted by half (1:2), so my titer was originally 1:1.

Antigen Phenotype

The blood test for dad that determines if the baby is at risk.

This test determines dad’s antigen status and will give you two letters. You’re looking for something that says EE or E+e-. However the results are phrased, it should tell you about Dad’s antigen pair, not just one letter. This test absolutely should not be an antibody screen like they do on pregnant women. Below are some examples of the right test and the wrong test that were run on actual dads and shared in the support group with permission. If Dad is negative for the antigen, then he cannot pass it on to the baby and the baby is not at risk for HDFN.

For example, when mom has anti-E:
If Dad is EE = 100% of babies with this partner will be at risk for HDFN.
If Dad is Ee = Each baby has a 50/50 chance of inheriting the E antigen and being at risk for HDFN.
If Dad is ee = all babies with this partner cannot inherit the E antigen and will be safe from HDFN.

CffDNA Testing

The simple blood draw for mom that determines if the baby is safe or at risk for HDFN.

If you have anti-D, anti-C, anti-c, anti-E, anti-e, or anti-K you have another optional blood test. This test can save you time, money, and unnecessary stress. It is called the cell free fetal DNA test or cffDNA for short. This is a blood test where they take mom’s blood and find tiny bits of baby’s DNA in it. The DNA is isolated and they are able to identify baby’s blood type and antigen status (as well as boy/girl). This test is wonderful for women whose antibodies may have come from a transfusion, and for those with heterozygous partners. Unlike an amniocentesis, this test does not carry the risk of fetal loss, infection, or worsening antibody levels. If a woman with anti-K has this test done, and it comes back that baby is Kell -, then she does not need extra appointments, costly ultrasounds, or the added stress of an alloimmunized pregnancy. She can have a perfectly normal pregnancy and delivery. Again, if baby is negative for the antigen that matches mom’s antibody, then baby will be safe. 

In the US the test is called the Unity Screen (for anti-D moms only). You also have the option of sending blood overseas to the UK or Netherlands. cffDNA testing is now being done in Australia as well as some parts of Canada. Visit the cffDNA page for more information about testing around the world including instructions and forms.

Invasive Testing Options


The invasive option for determining baby’s antigen status.

Amniocentesis (amnio) is a procedure where they remove some of the fluid from around baby to check baby’s blood type and antigen status. This is usually done between 14 and 20 weeks of gestation. Amniocentesis is usually done in the hospital, but some doctor’s offices and outpatient facilities are able to do it as well. For women with anti-D, anti-c, anti-C, anti-e, anti-E, and anti-K, amniocentesis is being replaced by noninvasive cffDNA testing which does not carry additional risks.

How is it done?
The doctor will perform an ultrasound to see where the baby is and to guide the needle. He will clean your abdomen and insert a thin, hollow needle into the uterus. A syringe will be used to take a small amount of fluid and the needle will be removed. You will need to stay still during the procedure. You may notice a stinging sensation or some cramping. The procedure usually takes about 20-30 minutes. Afterwards, baby will be monitored for a few minutes to check on heart rate. Talk with your doctor to find out about any physical restrictions and warning signs to watch for 14.

What risks are there?
Amniocentesis has replaced chorionic villus sampling (CVS) when it comes to alloimmunization. It is considered safer, has a lower risk of increasing antibodies than CVS, and more accurately addresses the information that doctors need to know. Amniocentesis carries some risks include miscarriage (1 in 300-500 in the 2nd trimester, possibly higher if done earlier), needle injury (if baby moves into the path of the needle), leaking amniotic fluid, development of new antibodies, an increase in titer levels, and infection.  For some women, the risks of amniocentesis are not worth it. It is possible to work with your doctor to have additional monitoring and treat the pregnancy as if it was affected and avoid the amnio altogether.

Additional Monitoring

MCA Doppler Scans

The special ultrasound that checks for fetal anemia.

The MCA Scan is a special type of doppler ultrasound, called a Middle Cerebral Artery (MCA)  scan, that is used to detect fetal anemia. This is a doppler assessment of peak velocity (PSV) in the mid cerebral artery. MCA scans are done before 38 weeks however after 35 weeks there is a higher risk of getting a false positive (saying baby is anemic when he actually isn’t).

MCA scans can be done anywhere ultrasound scans are done as long as the machine (and technician) are capable. Getting an accurate reading can be difficult, so it is very important that the physician or technician who is scanning is experienced in doing MCA scans.

How often an MCA is done depends on each individual case. Medical literature recommends MCA scans every 1-2 weeks if the fetus is at risk for HDFN . In general, when the MoM value from the scan reaches 1.4, women are rechecked in 1-3 days. When a woman has a 1.5 MoM, she is usually rescanned the next day and prepared for an immediate intrauterine blood transfusion.

How is it done?
MCA scans are done on your belly just like any other ultrasound. There is a certain angle that the technician needs to get to measure the blood flow in the correct artery of the brain. You will probably see red or blue on the screen since the colors indicate blood flow. Not all technicians are as skilled as others, or as the doctor. You can have different numbers from different techs at the same time. It is always a good idea to go with the numbers from the most experienced person (frequently the doctor). They will usually take an average of 3-5 readings to make sure they get a full picture.

What do the numbers mean?
With an MCA scan, you will get PSV values. Ask for them if they aren’t given, or look at the screen during the scan. These PSV values are then plugged into a formula to find your MoM number. You can get a great calculator here: A MoM of 1 is normal. An MoM of1.5 or higher is considered anemic.

What risks are there?
There are no additional risks with an MCA scan. It is important to note that MCA scans are not fully accurate after a transfusion. It is not uncommon to get false high readings after a transfusion. There is also a greater chance of getting a false high MoM if the baby is moving or over 35 weeks.

Don’t forget to get a copy of the printable care record to keep track of your results. The care record is a collection of documents you can use to keep track of your own care. Print it out and take it with you to all appointments. It has places to record titers, PSV and MOM values, and more.

Biophysical Profile (BPP)

The weekly ultrasound that all women with antibodies receive from 32 weeks onward.

A Biophysical profile (BPP) is a part of the ultrasound that can be added on if the doctor chooses. It takes 30 minutes and looks at 4 main areas: breathing, gross body movements, muscle tone, and amniotic fluid. Biophysical profiles can be done any time after the age of viability (24 weeks), but usually do not begin until after week 27.

A biophysical profile is used to evaluate and monitor a baby’s health. The goal of a biophysical profile is to prevent pregnancy loss and detect fetal hypoxia — when the baby is deprived of an adequate oxygen supply — early enough so that the baby can be delivered and not sustain permanent damage 7. Since this is always a risk with antibody pregnancies, most women will have at least one done.

Biophysical profiles can be done once during pregnancy, or more frequently depending on each individual case. Some doctors have them done once a month, every week or twice a week near the end of pregnancy.

How is it done?
A Biophysical profile is done just like a regular ultrasound, except they look for a couple of extra things and assign a score to the baby.

What do the numbers mean?
There are 8 points possible, 2 points are assigned for each category. It is an all or nothing score (2 points or 0 points).
Breathing: 1 or more episodes of fetal breathing lasting at least 30 seconds.
Gross Body Movement: 3 or more discrete body or limb movements.
Fetal Tone: One or more episodes of active extension and flexion of an extremity or opening and closing of the hand.
Amniotic Fluid Volume: A 2 x 2 centimeter pocket of amniotic fluid is present.
In this case, a perfect score is 8. Some places add on an extra category to give a possibility of 10 points. If so, they are adding a Non Stress Test (NST).
NST: 2 or more heart rate increases of at least 15 beats per minute. Each increase lasts 15 seconds or more and is seen with movement8.  

8 to 10 points means that your baby is healthy. A score of 6 to 8 points means that you may need to be retested in 12 to 24 hours. A score of 4 or less may mean the baby is having problems. Further testing will be recommended 8. A low score may mean that you need extra monitoring, early, or immediate delivery 7.

In this photo you can see the BPP results. The top has the pertinent info such as gestational age, estimated due date, etc. The middle contains the measurements of amniotic fluid (in this case, they were low at 8.4). Fetal heart rate is listed, as well as the final BPP results. There were 4 categories included: fetal tone, fetal breathing, fetal movements, and amniotic fluid.

What do the numbers mean?
There are 8 points possible, 2 points are assigned for each category. It is an all or nothing score (2 points or 0 points).
Breathing: 1 or more episodes of fetal breathing lasting at least 30 seconds.
Gross Body Movement: 3 or more discrete body or limb movements.
Fetal Tone: One or more episodes of active extension and flexion of an extremity or opening and closing of the hand.
Amniotic Fluid Volume: A 2 x 2 centimeter pocket of amniotic fluid is present.
In this case, a perfect score is 8. Some places add on an extra category to give a possibility of 10 points. If so, they are adding a Non Stress Test (NST).
NST: 2 or more heart rate increases of at least 15 beats per minute. Each increase lasts 15 seconds or more and is seen with movement 8.  

Nonstress Test (NST)

The weekly test that all women with antibodies receive after 32 weeks.

A nonstress test is a monitoring tool where they put 2 “buttons” on mom’s belly to monitor heart rate and uterine contractions. The sensors are hooked up to a machine that will print out a graph with baby’s heart rate, mom’s heart rate, baby’s movements, and uterine contractions. It is basically just monitoring baby’s heart rate for an extended amount of time, usually about 20-30 minutes, and can tell if additional tests are needed to check on the baby’s health. NSTs are done in the doctors office or hospital any time after 26 weeks, though most women with antibodies start receiving this weekly test at 32 weeks.

What do the numbers mean?
If the line is relatively flat, it is considered nonreactive. This is sometimes referred to as baby sleeping. They will try and wake baby up by having mom drink juice or eat something. They can also use a buzzer on the belly to startle the baby and get movement. In order to pass the NST (reactive), you need 2 or more heart rate increases of at least 15 beats per minute. Each increase lasts 15 seconds or more and is seen with movement 8.  

In the photos, the baby’s heart rate is the top line, mom’s heart rate is the faint middle line, the dotted line is the baby’s movement (more visible in the reactive picture), and the bottom line is the uterine contractions.

Additional Information
Because babies with HDFN can gradually become anemic, they can compensate for the anemia. This makes it so that it is possible for baby to still pass an NST and still be anemic. It’s important to always pay attention to movement, and notify your care provider and/or labor and delivery if you notice decreased movement.


  • We try to cover as much as possible so you can be informed about both current and past testing options. Individual doctors may or may not use some of these things. They choose the care plan that they (and you) are most comfortable with; we just provide information for your personal understanding about what has been used successfully in the literature.
  • With proper monitoring, you have every reason to expect a live baby.
  • You are your baby’s biggest advocate. If you do not feel like your needs are being met, seek a second opinion.
  • You can have a perfectly healthy baby when this is over. 
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