The one about the difference between TTTS and TAPS

You get so much medical jargon thrown at you when you’re diagnosed with a disease like TTTS and TAPS – and sometimes it’s really hard to process it.  There’s a lot of medical terms and it’s quite overwhelming.  People start talking about DVP’s and MCA’s and cord flow and start talking about amnios and lasers and SFR … it’s confusing and overwhelming.

For the purpose of this post, I will only be referring to identical twins who share a placenta. There are always exceptions to every rule, but the key to this post is simplicity.  So on that note, I am specifically referring the most common denominator – identical twins, sharing a placenta.

This is TAPS. The baby on the left is anaemic, the baby on the right polycythemic. Emmy and Tilly are well known as the “TAPS twins”

Let’s imagine, for a moment that you have 2 swimming pools, hooked up to one pool filtration system.    There are connections in the filter system that lets water move between the pools as well, so that everything is balanced and the water levels are the same –  Everything looks fantastic.

The swimming pool filter represents the placenta, the water represents the blood.

This is essentially how a modi twin pregnancy works.  You have 2 babies, in separate amniotic sacs, sharing 1 placenta with small connections between each other.  The babies are in fluid filled sacs, which they effectively breathe in, and then pee out.  The placenta helps filter the waste, as does the babies developing livers,  kidneys, and bladders.  They move blood between each other as well, sharing nutrients via the connections in the placenta and when everything is good, the babies grow and develop normally.

So here’s where the difference between TTTS and TAPS becomes important.  Let’s go back to the swimming pool image for a moment.

All of a sudden, there’s a fault with the filter system – and the water between the pools starts changing levels.  The first pool starts to lose water to the second pool, which is getting deeper and deeper, because the connection in the filter has become a one way street for the water.   The first pool is losing water and has much less to swim in, whilst the second too much water, and the pool could possibly overflow.

TTTS happens when the connections between the placenta are faulty – and only let blood flow one way between the twins.   This places an overload on the twin receiving all the blood, as their developing kidneys and bladder are having to process so much more blood and filter waste out.  They produce more and more pee,  where the other baby loses a lot of nutrients and can become restricted in their growth.  They also do not produce enough pee, and this means less fluid for them to swim in and develop. They generally end up being squashed by the other twin’s excess fluid, and it makes it hard to see them on ultrasound.

The rapid growth of fluid is often felt by the mother, and is considered a warning sign that TTTS is occuring.  With too much fluid also comes the issue of the water breaking and early labour.  I’ll go into warning signs later though.

The biggest risk is with the twin in the smaller swimming pool though. Without enough nutrients or water, their kidneys and bladder shut down, and they can no longer filter waste.  There are risks to the other twin, without any doubt, with internal bleeding and heart failure being the biggest due to having too much blood.

TTTS can be detected on an ultrasound, and is usually signified by the following :

  • Unbalanced fluid between the twins on ultrasound.  One twin will be in a large sac of water, the other, with very little fluid.
  • An absent bladder on the donor twin (the one with little fluid)
  • Unbalanced blood flow and fluid retention

There are also signs that you should be aware of physically

  • Sudden weight gain, and fluid retention
  • Feeling like you grew “overnight” with a tight belly, and sometimes shortness of breath
  • Contractions, fluid loss or bleeding
  • Not feeling both twins moving as much as normal.

It is important that you are aware of any physical changes, and report these to your doctor ASAP.

This is the simplified story of TTTS.

So let’s now talk about TAPS, and let’s go back to the swimming pool imagery.

The swimming pool is set up the same way here – 2 pools, one filtration system with connections between the pools that move things between them.

Let’s work this time on the pools being full of water, but also filled with small balls.   When the filter system is working normally, you can move freely in the pools even with the balls in there, because they will pass backwards and forwards between the pools with no problems.

However, something goes wrong with the filter – and the balls slowly start moving to one pool, but not coming back in. The water still flows freely. The connections have again become a one way street – and one pool has hardly any balls, and you can swim freely and easily, but the other pool is now so full of balls, that you can’t move at all. The levels of water are still the same, but the water on one side has become denser over time,  with more balls than the other side.  

In this situation, the water still represents blood, but the balls represent red blood cells passing between the twins.

This is TAPS.

The scenario above is a very simplified version of what happens.   With TAPS, the connections between both halves of the placenta are less than 1 millimetre thick.  The only thing that passes through them is red blood cells.  You will have one baby with too many red blood cells (called polycythemia), which makes their blood so thick it’s like tomato ketchup (the pool with too many balls), and the other baby with too few red blood cells, which makes their blood more like rose wine (the pool with few balls).

The biggest difference with TAPS and TTTS is simply this – TTTS can be seen on a normal ultrasound due to the fluid imbalance.  TAPS cannot be seen because it does not affect the fluid levels. It is also a longer, slower process than TTTS.

TAPS can be suspected when the babies are in the uterus, and is generally confirmed post birth when the babies are born one red, one white.

One red, one white. Our girls at birth. The red colour comes from polycythemia, an excess of red blood cells caused by TAPS.

There are no external warning signs for TAPS for the mother.

This is where appropriate pre-natal care comes into play. TAPS can be suspected via testing the flow of blood in the mid cerebral artery in the brain (or MCA).  If the blood moves too quickly in one baby, and too slowly in the other baby, there is a possibility that they are developing TAPS.  Monitoring these readings is vital as part of every checkup.  Sometimes, on ultrasound, the heart may appear enlarged from pumping around blood that is too thick as well.

Post birth, the placenta can be injected with dye to check for the tiny connections.  It is also vital to check the haematocrit (red blood cell) levels of the babies to confirm the diagnosis.  (An example – a normal newborn has a level of between 55% and 62%. My recipient was born with haematocrit levels higher than 80%)

TAPS can cause the donor’s heart to fail, or retain too much fluid.  The recipient may have poor circulation, which can also cause internal bleeding.   It is also vital after birth that the babies are treated for the anaemia and polycythemia – this can include for the donor, blood transfusions, and for the recipient, blood being taken from them, and their blood being thinned with intravenous saline.

This is the simplified story of TAPS.

It’s important that if you are having modi twins to find a doctor who will monitor you regularly, every 2 weeks being ideal.  They will check the fluid levels between the babies, making sure that they are within balance, check the bladders and hearts of both babies, and check the cord flow for each baby to the placenta.  It’s also important to insist on them checking the doppler readings on the mid cerebral artery – as said above, there are so few indications that your babies might have TAPS.  It’s also important to discuss delivery before 37 weeks, as the placenta starts to work overtime towards the end of the pregnancy, with the demands of 2 babies.

Some questions you might have –

I had a red and white set of twins – does this mean I had TAPS?

It’s entirely possible.  However, bear in mind that TTTS also can result in a red and white twins combination.  (Remember, TTTS is also caused by too much blood in one twin, the difference is that TAPS is too many red blood cells only).  If, when your babies are born, you have a red and white pair, insist that they test their blood for the haematocrit levels.   This will help with the necessary treatments for polycythemia and anaemia)  Without these readings though, it’s virtually impossible for the man on the street to say yes.  Remember, TAPS is a silent disease – there are not many external signs it is happening.

It is also important to remember that TAPS is not acute end stage TTTS.  It is caused by connections less than one millimetre, and over a long period of time. TAPS requires different handling due to the density of the blood in the recipient.

Can I do anything to prevent TTTS or TAPS?

In a nutshell, no.   There is no surefire treatment that can prevent either disease.  You’ll see around the internet about increasing your protein intake, but there is little conclusive evidence of this being a surefire remedy.  Mothers of multiples often have an increased demand on their bodies due to growing 2 babies, so the extra protein is always a big help for sure.  But preventing TTTS and TAPS?  It’s not studied enough.

There are therapies that can help once TTTS and TAPS are diagnosed, with the most common being laser therapy.  If you are diagnosed, discuss all treatment options with your doctor, and make an informed decision.

I don’t know what the doctors should be looking for, can you help?

It’s important here to get someone who has experience with twins.  Ideally, the doctors should be establishing early if your twins share a placenta, and how many amniotic sacs there are.

Every 2 weeks, they should be checking the fluid levels of each baby, and monitoring this closely.  They should be checking the growth of the babies, as well, checking their organ function (with bladder and heart being important.).   They should be checking the flow of blood in the cord, checking the number of blood vessels in the cord also.  They should also be checking the blood flow of the babies in the mid cerebral artery, for signs of polycythemia (thick blood with too many red blood cells) and anaemia.   I also always advocate that if you are unsure of what is going on, or you feel uncomfortable, ask questions of your doctors.  It’s ok to ask questions, or to ask them to explain things in a different way.  These are your children, your body,  you have to be able to be comfortable with the information you are given.

I don’t think I’m getting appropriate care – what can I do?

There are many online groups, many online organisations that can direct you to skilled and appropriate medical help.  You can also educate your doctors about both diseases, and don’t be afraid to challenge or ask for a second opinion.

Can I ask you more questions?

Absolutely. That’s what the comments are for.

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