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Should be answered at least weekly at each ultrasound
1. Is the cervix long
and closed, or is it thinning or dilated?
The cervix has an ultrasound
measurement in
centimeters when it is long and closed. You
want to understand what number is normal and
at what number a cerclage (stitching of the cervix
to make it stronger) might be needed to help give
the cervix support. Knowing the relevance of the measurement,
parents can understand what they
would be looking for at each appointment and why
they can feel positive if the length of the cervix is not
changing. Often we find that looking at the cervix
frequently is often not done. Many pregnancies could
have been saved by simply doing this test at each appointment.
Because of the nature of TTTS,
specifically polyhydramnios, in addition to a
multiple pregnancy, the cervix is at risk to weaken.
Laser surgery can still be done after a cerclage,
but not after a premature birth and loss of the
babies from a cervix that weakened without
notice. Long and closed is defined as 4-5
centimeters. When this number gets below 3,
it may be time to do a cerclage. This shows
that the cervix is 'thinning' or 'funneling' or
'shortening' and you want to help stay pregnant
with the cerclage.
2. Is the recipient's heart thickening?
This is another sign that laser
surgery may be
needed. Thickening of the heart shows
increased stress for the recipient twin from the
increased volume of blood into his or her
cardiovascular system.
3. What is the biggest pocket of fluid
around each baby?
This is another form of measuring
the fluid in
each baby's sac. The normal range being
between 3-8cm. You can determine the level
of severity of the fluid problem by watching what
the numbers are doing and how much they get
out of the normal range. Again, it is about helping
you know when you might need to start a treatment
and why. These measurements will make sense to
you and will give you the tools to make decisions.
There is disagreement concerning at what number
would an amniocentesis be done. Experts feel you
need to be very careful about putting a needle into
the uterus and it should be for a good reason. It
does not make sense to do an amnio for genetic
reasons, the babies are always healthy. It may
also not make sense to do an amnio if you are
measuring 8-9cm as the biggest pocket of fluid.
It may make more sense to wait until the number
is more like 10 or 11cm. Then you know they will
be draining off a lot of fluid and will have good
reason to enter the uterus with a needle.
4. What are the weights of the babies?
We tell parents that anything
over a 20% size
difference between the babies is of concern
and the doctors start to ask why. Babies are
never going to be the same size but over 20%
is unusual and has a reason to it. Both placental
share and the number and direction of flow of the connections
are important in getting the answer
of why this is happening. To get the size difference between
your babies, know the weights of the
babies, subtract them and divide by the bigger
number. This is the percentage size difference.
Babies can be different in size because one has
more placenta to start with than the other, or they
could share the placenta 50-50 but the connections
in the placenta are causing the size difference, or
it can be a combination of both. You cannot tell for
sure what the placental
share is until after birth.
5. Can you see the bladder of the
donor baby?
The bladder is there, but the
question is 'can we
visualize it?'. When the baby does not get enough
blood flow, it may not be urinating enough to see
the bladder. You need to watch for at least 30
minutes during the ultrasound. If the perinatologist
tells you that the biggest pocket of fluid for the
donor is 2cm and you can see the bladder,
that is much better than not being able to even
get a 1cm in the donor's sac or not being able
to see a bladder. This will help give you some
perspective of how the little one is doing and
where you are in the diagnosis of the syndrome.
6. Does the recipient twin have hydrops?
Hydrops is when you see fluid
inside the recipient
baby's body on ultrasound and it is a sign of
beginning heart failure. We have seen babies
live and be healthy with hydrops. In fact, it can
completely reverse after laser surgery with time. Amniocentesis
may not go to the source of the
problem or do it fast enough to help this turn
around. Knowing what defines hydrops is helpful
because you will be relieved each visit when your
baby does not have it. If at one appointment
hydrops is seen, you will know what to do.
You would have already made that decision in
your backup plan that you have created or will
be creating. Beware that some physicians will
only advise termination of a baby with hydrops.
7. Is the smaller baby growing at the same
rate of growth?
It is important for you to understand
placental
share issues. If a baby has a small placental
share, at some gestational week the baby will
start to 'run out' of his share of the placenta.
This is a gradual process, but what it means is
that the baby wants to get bigger in size, but it
is not getting enough nutrients to do so from
his or her share of the placenta. When the donor
baby stops growing, this is the time to deliver.
If you try to 'buy more
time' the baby will only be
deprived of oxygen and could end up with varying
degrees of cerebral palsy. Watching the rate of
growth is another reason for frequent ultrasounds.
If your recipient baby does not have polyhydramnios
(too much fluid) but there is over a 20% size
difference in the babies, they may have the
syndrome but it might be more mild. The size
difference is probably coming from the fact that
one has more placenta to begin with than the
other. In this situation, many mothers have
benefited by going into the hospital at 24
weeks for 24 hour monitoring of the smaller
donor baby. Usually the parents deliver
around 28-30 weeks when they see one or
both babies going into distress, the donor
from lack of growth. At some point, the babies
may be better off in the care of the miracle
workers of the NICU than continuing in the
environment of a shared monochorionic placenta.
8. Is the Doppler normal for each baby?
The Doppler is a test of how
the blood is
flowing through the umbilical cords of the
babies and how well their hearts are pumping
the blood. This test is done during an ultrasound.
You then will see peaks or mountains crossing the
screen. The question is does the baby have absent diastolic
flow (the baby's heart is not going through
the resting stage of a heartbeat) or does the baby
has reverse flow (the blood is leaving the baby's
heart, then regurgitating back into the heart).
How it works is, when the heart squeezes and
contracts it is called systole and when it rest,
relaxes and fills it is called diastole. When the
donor babies go into to distress, they lose that
diastolic flow (the resting phase of the cardiac cycle).
This means their hearts are pumping and pumping
without resting. If the donor baby has absent
diastolic flow, laser surgery may help. We have
seen babies go weeks and weeks with this
problem and survive, but they are very tired and
in need of a lot of help in the NICU. It would be
better for the baby to get treatment to help the
flow go back to normal. Reverse flow is more
dangerous, seen mainly with recipient babies,
and you need to know that urgent decision
making needs to take place with laser surgery
being our choice if possible. Doppler tests can
and should be done from 18 weeks and at each
weekly ultrasound.
9. What is the fundal height?
The fundal height is one way
to measure in
centimeters how much fluid is 'too much' in the
sac of the recipient twin and 'too little' in the sac
of the donor. Instead of saying 'too much' or 'too
little' fluid when talking about the sacs, you need
to find out the fundal height measurement to
understand the fluid problem. The fundal height
for twins is normally 2-3 centimeters more then the gestational
week you are at. If you are 18 weeks
pregnant with a fundal height of 21cm, this would
be normal for twins. We have helped mothers at
18 weeks with a fundal height of 45cm to give you perspective.
This would be like being beyond full
term and shows a more serious fluid problem.
Knowing this number will help you understand
what number they are looking for to need laser
surgery or amniocenteses.
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