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Week By Week in an Alloimmunized Pregnancy


Essentials- For those who have had a previously affected pregnancy, a preconception appointment with your MFM, or potential MFM, can be helpful. If you had a severely affected pregnancy or lost a baby to HDFN in the past we strongly recommend having a preconception appointment with an MFM before attempting another pregnancy.

During your preconception appointment you can discuss any questions or concerns you may have about a future pregnancy. You can work together with your MFM to create a care plan that you and your partner feel confident about. Having a face to face meeting with your MFM also helps you get a feel for the MFM’s bedside manner and how you both interact with each other, how your MFM handles questions from you. For those who have lost a baby to HDFN, the preconception appointment is a good time to ask your MFM questions about your experience and discuss ways to prevent another loss.

Click HERE for a list of possible preconception questions to help guide you through your appointment.


Be Aware:

It can be helpful to check your antibody titer during your preconception appointment, just to get a starting point, but be aware that titers often change once a woman becomes pregnant. Your titer before pregnancy is not an accurate predictor of how your pregnancy will go or how affected your baby might be.


Silver Lining:

No one is in danger at the moment so you can rest easy and focus on making a good plan for the future. You can choose an MFM that you feel confident about, BE PICKY. 


Conception- 7 Weeks



Antibody Screen and Titer Check- You should be given an antibody screen and your titers should be checked.

Dating Ultrasound- Early ultrasounds are the most accurate for dating purposes so it is helpful to have a dating ultrasound, especially if you aren’t sure about the dates of conception or your last menstrual period. Knowing baby’s accurate due date is very important during an allo pregnancy since many of the essential monitoring and treatments are based on gestational age.

First MFM Appointment- If you have had a previous severely affected pregnancy or have lost a baby to HDFN, or if your titers are in the hundreds or thousands, it is recommended that you have your first appointment with your MFM as early as possible. Certain treatments such as plasmapheresis and IVIG, must be scheduled during this time period and can take weeks to be approved by insurance companies. These treatments are very time sensitive and are most effective when started by a certain gestation, so getting in to see your MFM early in the pregnancy is a great way to keep your baby safe.


Be Aware: 


Silver Lining: Your baby is completely safe from your antibodies at this point. Red cell antibodies cannot harm the baby during this time period so rest in the fact that your baby is safe from your antibodies right now.


8-12 Weeks


If this is your first sensitized pregnancy, or first pregnancy with your partner, now is the time to have your partner’s blood tested for the antigens. The baby’s father should be phenotyped for any of the matching antigens that you have antibodies to. For example, if you tested positive for anti-Kell antibodies, your partner needs to be tested for the Kell antigen. This test can be done by your MFM, regular OB or your partner’s regular doctor.

You should be arranging your first MFM appointment now.

If you have anti-D antibodies, you can have the cell free DNA test to learn whether baby is positive or negative for the D antigen.

For those having plasmapheresis and IVIG treatments, plasmapheresis is recommended between 10-11 weeks and IVIG should start immediately after plasmapheresis is finished (11-12 weeks.) Usually a port or permacath or both are surgically implanted before starting treatments.


Be Aware: Sometimes even medical professionals get confused about the difference between antigen and antibodies. MAKE SURE that the baby’s father is tested for the antigen, not the antibody. A best practice is to ask for his test results in writing either on paper or through his online patient portal so that you can see for sure that he was tested for the right thing. Future monitoring and treatment procedures are based on the results to tha baby’s father’s antigen test, so it is very important that he receives the correct test. 

Silver Lining: It is still too early for your baby to be affected by your antibodies, so try not to worry about how your baby is doing.


13-18 weeks


Lots of essentials for this gestation

First MFM appointment: By the end of this time period you should have already had your first appointment with your MFM.

Father’s Antigen Status- You should know or find out baby’s father’s antigen status- Positive or Negative for the antigen? Homozygous or heterozygous for the antigen?

Fetal Cell Free DNA Test- If you have anti-Kell, E or c antibodies we recommend the free cell fetal DNA test that can be done at 14 weeks and on. It is a reliable, non-invasive way to find out your baby’s antigen status. If baby is antigen negative, then your antibodies cannot harm your baby. If baby is antigen positive you and your MFM will know to keep a closer eye on baby throughout the pregnancy.

First MCA Scan- Probably the most important essential for this gestation is the start of MCA scans. If you have a critical titer you should start weekly MCA scans by 16-18 weeks. If you have anti-Kell it is a good idea to still have mca scans even without a critical titer since Kell has been known to affect the fetus even with low titers. 

Be Aware: This is when baby could become affected by maternal antibodies in the most extreme cases. Some common misconceptions you might hear are:

 “Babies can’t be affected by the antibodies before 19/20 weeks.” 

“Nothing can be done to help anemic babies before 19/20 weeks anyway so no use scanning that early.”

“Scans before 18 weeks are not accurate or are too difficult to perform.”

“There aren’t any accurate MCA-PSV values earlier than 18 weeks/ The MCA-PSV calculator only starts at 18 weeks, therefore no need to start MCA scans earlier.” 

Silver Lining: You have made it to the second trimester! This is a big milestone to celebrate! The risk of having a miscarriage (unrelated to the antibodies) is much lower now that you are out of the first trimester. 

By the time you reach 15 or 16 weeks, there are treatment options for babies who become anemic in utero. Even though the risks are higher at such early gestations, IPTs (intraperitoneal transfusions) can be performed by experienced professionals as early as 15 weeks. 

MCA Scans can now be performed so you and your doctor can now know whether baby is being affected by the antibodies or not by having an MCA doppler scan. 

19-22 Weeks

Essentials: If you have a critical titer you should now be having weekly MCA scans. 

If you do have a critical titer, you should talk to your MFM about IUTs. What is their protocol if the MCA scan reaches 1.5 or over? Who would perform the IUT? Would you be referred to another facility for IUTs? How many IUTs has the provider performed in the past year? What is their success rate? 

Be Aware: Some care providers consider 22 weeks to be the point of viability. Other care providers consider 23 or 24 weeks to be the cut off for viability. This is important to discuss with your MFM ahead of time so that you can have a plan in place in the rare instance that baby would need to be delivered at 22-24 weeks (For example, if baby went into distress during an IUT) 

Silver Lining: IUTs get easier and safer as baby grows. By now, physicians performing an IUT are usually able to do an IVT (intravenous transfusion) instead of only relying on IPTs (intraperitoneal transfusions.)

23-27 Weeks

Essentials: Consider setting up a tour of the NICU if you think that might help prepare you for birth. 

Be Aware: Now that baby is viable, your MFMs might be considering using steroids to help develop baby’s lungs if baby starts showing signs of fetal anemia or if an IUT is coming up. Be aware that steroids can artificially lower MCA scan results. The best course of action is to only administer steroids when MCA scans are no longer necessary. 

Silver Lining: Your baby is now considered viable and could possibly survive outside of the womb if born now. This is a huge milestone to be celebrated! Every week longer in the womb means a higher survival rate for baby. 

28-33 Weeks

Essentials: If you haven’t already, discuss your delivery plan with your MFM or OB. Pack your hospital bags. 

Be Aware: 

Silver Lining: You have now reached the third trimester! Congratulations! Another huge milestone. It is a huge relief to know that it is possible to deliver baby now if there was a problem in utero.

34 - 40 Weeks

Essentials: Delivery recommendations, what to pack, how to prepare for labor and delivery, 

Be Aware: MCA scans become less reliable after 38 weeks, which is why it is recommended for allo moms to deliver by 37-38 weeks unless baby is antigen negative. 

Silver Lining: Your baby can now be delivered with little to no preemie issues to deal with. You made it! 

Delivery and NICU

Essentials:list of tests for baby, bili calculator, etc.  

At the time of delivery your baby’s care shifts from the MFM to the neonatologists/pediatrician. This can sometimes come as a sudden jolt after being cared for by your MFM for months. Many specialists and clinicians have little experience treating babies with HDFN. Go in expecting to be an advocate for your baby. Even though your baby has received months of monitoring and possibly treatment in utero, your baby is born without a medical record. YOU have to be your child’s medical record. Remind your baby’s physicians that they are dealing with hemolytic disease of the fetus and newborn. Remind the physicians that the journey your baby just took in utero does have an effect on what type of monitoring and treatment is required now to keep your baby safe.

Delayed cord clamping

Be Aware: Hemolytic anemia is different from iron deficiency anemia (the type most doctors encounter) and hemolytic jaundice is different from newborn jaundice (the type most doctors encounter.) Hemolytic jaundice must be monitored more closely and treated more aggressively. Hemolytic anemia is not resolved with an iron supplement. Your baby is also at risk for delayed onset anemia if the coombs test at birth was positive, even if baby did not need IUTs, even if baby’s hct/hgb are completely normal right after birth. 

Yes, breastfeeding is safe. 

If your baby has had IUTs, it is very likely that the majority (or all) of your baby’s blood will be donor blood since all of the antigen positive blood has been destroyed by your antibodies already. This means that baby will probably be born with a blood type different than his actual blood type. This also means that the newborn screening is actually done on donor blood and not on your child’s actual blood. Make sure to schedule a repeat newborn blood screen test for several weeks after birth (when baby has cleared out the donor blood and replaced it with his own blood.) Also, don’t be too worried if your child’s original newborn screen comes back as abnormal. There have been cases of HDFN babies showing extremely low levels of carnitine on their newborn screening. All of these babies had had IUTs. The mothers were informed that their babies could have an inherited metabolic disorder called “Carnitine Deficiency Disorder” or “Carnitine Uptake Disorder.” When the babies were given repeat newborn screen blood tests several weeks later, all of their carnitine results were normal. No studies have been done to determine what caused the baby’s donor blood to be so low on carnitine. 

Silver Lining: Your baby is here! Congratulations! Even though baby might need more monitoring and treatment, it is much easier and safer to treat baby on the outside than in utero. 

Post Discharge

Essentials: Follow up blood work, follow up hearing tests

Be Aware: After being discharged from the hospital parents and doctors still need to keep a close eye on babies with HDFN, especially in the days and weeks after being released. Since our babies are transferred from MFM to neonatologist to pediatrician it is common for information to fall through the cracks along the way. If your baby had a coombs positive blood test at birth, they are at risk for delayed onset anemia. They should be given weekly blood tests to check hematocrit/hemoglobin and retic. Once baby’s hct/hgb are stable or rising for two consecutive weeks, you can stop blood tests and baby is in the clear.

 Tooth enamel, neutropenia, delayed onset anemia

Silver Lining: Baby is done when cleared from hematology, baby snuggles, relief