Hi, folks.
Today we're going to be
discussing our twin pregnancies
and specifically the impact
of chorionicity
on the risk
of intrauterine fetal demise
in twin pregnancies.
So this presentation
was prepared by the authors
listed there, who at the time
were second-year Duke NUS
medical students who had just
completed
their obstetrics and gynecology
clinical clerkship.
So what's the relevance
of twin pregnancies
to contemporary obstetrics?
Well, traditionally, it's
quite well known
that twin pregnancies are
associated with a poorer outcome
compared to singleton
pregnancies.
And it just so happens
that over the past 20 to 30
years,
there's been a dramatic rise
in the rate of twin pregnancies.
So you can see there,
both in the US and Singapore,
there have been quite marked
increases in twin birth rate.
And it was thought that this is
because of two main reasons.
One is the use of these ARTs,
assisted
reproductive technologies,
such as in vitro fertilization.
And such procedures
are associated with quite
a dramatic increase in risk
for twin pregnancy.
And also in recent years,
there's been a trend
towards mothers choosing to have
children at a later age.
And so an older maternal age
is also associated
with an increased risk
of twin pregnancy.
So when we're discussing
twin pregnancies, you will hear
the terms
chorionicity and amnionicity,
which relate to the number
of placentas
or the number
of gestational sacs,
respectively.
So you can see from this diagram
that you can have
a mono
or a dichorionic twin pregnancy,
which would have a single
or a double placenta.
And you can have a mono
or a diamniotic pregnancy,
where you will have a single
or a double gestational sac.
And for the purpose
of this current paper,
we'll mainly be focusing
on the monochorionic diamniotic
pregnancy
and the dichorionic diamniotic
pregnancy.
So these pregnancies
are the same, with the exception
that one will have
twin placentas
and the other will have
single placenta.
So you can see here
that depending on the time
at which you'll have cleavage
of the fertilized ovum,
you will have
a different placentation
for the twin pregnancy.
So cleavage at less than 72
hours following fertilization
will yield
a diamniotic dichorionic or DADC
placentation, whilst cleavage
between days four to seven
would yield
a diamniotic monochorionic
or DAMC placentation.
And that would form the majority
of monozygous twins, the DAMC
configuration.
And as you see,
if you have later and later
cleavage of the ovum,
eventually you'll have conjoined
twins rather or you'll have
cleavage of the ovum
after day 13.
And this would be the rarest
of the monozygous twin
placentations.
So I mentioned previously
that twin pregnancies are
associated with a poorer
maternal outcome compared
to singleton pregnancies.
And it was previously thought
that it was zygocity rather
than chorionicity that dictated
the risk for adverse outcomes
and twin pregnancy.
But it was later found that it
was chorionicity, or the number
of placentas, which dictates
the outcome
of the twin pregnancy
more so than zygocity.
And so monochorionic
twin pregnancies are known
to have a poorer outcome
compared
to dichorionic twin pregnancies.
So I've shown here a screen
capture of the article header,
which is entitled "The impact
of chorionicity on risk
and timing
of intrauterine fetal demise
in twin pregnancy."
And this was put out
in late 2012
by the authors indicated there.
And if you're
interested in looking up
the full text of this article,
you can use this screen capture
to help you do that.
So what was this article
all about?
Well, the authors indicate there
were two main aims
for this study, the first
of which
was to determine how
chorionicity relates to the risk
intrauterine fetal demise--
IUFD-- on one
or both of the fetuses.
So this was the main aim
of this paper.
They also mention a second aim,
which was to describe how
chorionicity where the mono
or dichorionic impacted the risk
and timing of a second death
in pregnancies where you had
a first death and then you had
a second death.
They wanted to look at how
that second death would relate
in terms of timing
and in terms of chorionicity.
This was a retrospective cohort
study done between 1990 and 2008
at Washington University Medical
Center,
examining
routine second trimester
sonographic [INAUDIBLE]
of twin pregnancies between 17
and 22 weeks of gestation.
The main outcome studied was
IUFD, as this was a study
of twin pregnancies.
Singleton and higher order
multiple gestations
were excluded.
Monoamniotic twins were also
excluded as monoamnionicity is
a confounding factor known to be
associated with higher risks.
Pregnancies complicated
by twin-to-twin transfusion
syndrome, or TTTS,
and fetal death before 20 weeks
of gestation were similarly
excluded.
Pregnancies
with incomplete follow
up were dropped from the study.
Data was retrieved primarily
from medical records
and supplemented
by patient-derived information
such as medical, obstetrical,
and social histories obtained
between 17 and 22
weeks of gestation.
The authors also looked
at any antenatal and delivery
complications
and at the neonatal outcomes.
The frequency of follow up
was three to four weeks
for all twins in the study,
with NST or BPP done twice
a week, starting from 32 weeks
of gestation.
In addition, monochorionic twins
were checked every two weeks
for TTTS.
If any evidence of TTTS
was found, that pregnancy
was excluded on the study.
These are the key definitions
used in the study.
Chorionicity was determined
by the earliest
available ultrasound
and confirmed
by pathology specimens
from some of the pregnancies.
Gestational age was defined
as the first day
of the last menstrual period.
If the gestational age
by the earliest ultrasound
dating deferred,
the gestational age
was reassigned according
to ultrasound dating using
the biometry of the larger twin
when dating the pregnancy.
IUFD, or intrauterine fetal
death,
was defined as fetal death which
occurred at least 20 weeks
into the pregnancy
and confirmed by ultrasound.
IUGR was defined as having
an estimated fetal growth rate
below the 10th percentile.
The data collected was analyzed
using [INAUDIBLE] software.
Analyses were run to compare
baseline characteristics
of the twin pregnancies
to overall relative risk
of IUFD,
the risk of IUFD of either twin,
and the prospective risk
of IUFD.
Pregnancies with double IUFD
were compared against those
with single IUFD
to identify other factors
associated with loss
of the second twin.
So this waterfall chart depicts
the flow of participants
in the study.
Over 18 years,
2,445 twin pregnancies were
scanned in total, of which 112
pregnancies were excluded.
The criteria for exclusion
included, one, pregnancies
of monoamniotic twin.
Two, pregnancies that had
twin-to-twin transfusion
syndrome.
And, three, pregnancies
with higher-order multiples.
Actually excluding pregnancies
with the aforementioned
exclusion criteria,
2,333 pregnancies were left.
Of that, 172 pregnancies were
lost to follow up.
But that still left 2,161
pregnancies with compete follow
up.
And of that, 1,665 were
dichorionic pregnancies and 496
were monochorionic pregnancies.
So as you can see, the ratio
of dichorionic to monochorionic
pregnancies was approximately
three to one.
Moving on to the results
of the study, it was found
that there is a higher risk
of intrauterine fetal demise
in monochorionic pregnancies
versus dichorionic twin
pregnancies.
When we look at the upper half
of the chart,
we see
that
the intrauterine fetal demise
risk in a dichorionic pregnancy
is 3.4%.
For a monochorionic twin
pregnancy, the risk of IUFD
is 6%.
With this in context, the risk
of fetal demise in a singleton
pregnancy in 0.6%,
but for a dichorionic twin
pregnancy, the risk is five
times more,
and for a monochorionic twin
pregnancy, the risk is actually
10 times more.
The adjusted odds ratio
for intrauterine fetal demise
in monochorionic pregnancies
versus dichorionic pregnancy
is 1.69.
The same holds
true for double fetal demise.
Looking at the bottom half
of the chart,
you see that the risk
of double fetal demise
in a dichorionic pregnancy
is 1.2%, whereas the risk
of double fetal demise
in a monochorionic pregnancy
is 2.4%.
And here the adjusted odds ratio
is 2.11.
This chart shows
the prospective risk
of intrauterine fetal death
by gestational age.
Note that the risk
at each gestational age
is the risk
for any intrauterine fetal death
for the rest of the pregnancy.
So for example, at 20 to 21
weeks,
the risk
of intrauterine fetal death
for a dichorionic pregnancy
for the rest of that pregnancy
is 6%.
And the risk
for an intrauterine fetal death
in a monochorionic pregnancy
for the rest of that pregnancy
is 3.4%.
As can be seen in this chart,
the risk
of intrauterine fetal death
in monochorion twins
is higher than dichorionic twins
before 28 weeks, after which
the risk
of monochorionic intrauterine
fetal death
actually falls below that
of dichorionic fetal death.
It is worth noting then also
that at 36 to 37 weeks,
the percentage of continuing
monochorionic and dichorionic
pregnancies
is comparable at approximately
50%.
However, there are
no intrauterine fetal deaths
after term.
The authors do not attempt
to explain these findings
and why beyond 28 weeks
the risk
of monochorionic fetal death
falls
below dichorionic intrauterine
fetal death.
This chart provides data
reporting the secondary outcome
of the study, which
is that double demise occurs
primarily before 24 weeks,
regardless of chorionicity.
In the chart, we have divided
pregnancies
in double fetal demise
according to the gestational age
of the second twin at the time
of the second twin's demise.
So if we look
at monochorionic pregnancies,
we find that 58% of pregnancies
with double fetal demise
had
their second twin intrauterine
fetal death occur before 24
weeks and then
75% of dichorionic pregnancies
with double fetal demise
the intrauterine fetal death
of the second twin
occurred before 24 weeks.
Now, we come
to the overall impression
of the paper's study.
The study was all done
in several [INAUDIBLE].
Firstly, this is a retrospective
study with large sample size
that supports the research topic
in question.
Again, the authors have also
taken good effort in adjusting
for characteristic mismatches
of the sample using statistics.
However, the weakness
of the paper mainly lies
in excessive study time frame
used.
Over 18 years, the practice
of management of twins
may have changed considerably,
hence influencing the outcome
of the pregnancy study.
There is also sample bias
because only twins from one
medical center were used
and also in characterizing
the confounders, authors choose
to use a yes or no method
instead of using
a continuous model.
The clinic value of the study
is rather limited.
This is because the research
outcome of the study
is largely unsurprising.
A paper published five years ago
has already shown the MCDA twins
tend to have poorer outcome
as compared to DCDA twins.
This study is also limited
because only one outcome, IUFD,
was studied, Leaving out
[INAUDIBLE] complication
of twin pregnancies
such as preterm labor, TRAP,
and TPTL.
In conclusion, this study
has shown that monophonic twins
carry an increased risk
of fetal death
compared to dichorionic twins.
And it has also shown
that double demise occurs
at primarily less than 24 weeks
regardless of chorionicity.
However, this limited amount
of clinical use for these
are provided in this paper.
The author used
a minimum publishable union
model to publish [INAUDIBLE]
available.
Other than that, the usefulness
of the outcome measure,
which is IUFD, may not fully
account
for the clinical practice
where the other outcomes
such as neurological effect
are not accounted.
Finally, the paper also studies
the second-order effect.
The twin pregnancy itself
already presents a higher risk
than the single pregnancy,
no matter
whether the chorionicity or not.
Last but not least, we
would like to take
this opportunity to all
the doctors and nurses
at [INAUDIBLE] hospital,
department O&G,
for volunteering their time
and expertise to help us.
Thank you.
