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\begin{document}

\title{Monochorionicity in the absence of TTTS is not associated with an
increased risk of adverse neurodevelopment at 5 years of age.}



\author[1]{Richard Brown}%
\affil[1]{McGill University, Montreal, Canada H9W 5A6}%


\vspace{-1em}



  
  \date{May 14, 2024}


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Monochorionicity in the absence of TTTS is not associated with an
increased risk of adverse neurodevelopment at 5 years of age.

Richard N Brown, MBBS, FRCOG, FACOG

Director of Obstetrics and Maternal Fetal Medicine, McGill University,
McGill University Health Centre, Montreal, Canada

Correspondence Address

Richard Brown, Division of Maternal Fetal Medicine, McGill University
Health Centre, 1001 Decarie Blvd, Montreal, Canada H4A 3J1

Richard.brown@mcgill.ca

Disclosures: none

Despite stabilising twin pregnancy rates over the last two decades, as
much as one birth in 30 is a twin birth. With twin preterm birth rates
being as high as 60\% (Martin et al, National Vital Statistics
Reports;2019:68), prematurity represents the major factor influencing
overall perinatal outcomes in twins. Monochorionicity (MC), with its
attendant unique complications (including twin-to-twin transfusion
syndrome (TTTS) and selective fetal growth restriction (sFGR)),
represents another major risk factor for adverse perinatal outcome in
twinning. MC complications contribute to the increased perinatal death
rate evident in MC twins compared to dichorionic (DC) twins, as well as
the greater premature birth rates {[}often iatrogenic{]} amongst MC
twins. The potential for neurological harm associated with TTTS is now
well understood, whilst in comparison that associated with growth
discordance / sFGR or monochorionicity itself, remains less well
established.

Existing data have suggested increased rates of long-term
neurodevelopmental deficits in MC twins overall and especially in those
with growth discordance. Perinatal care of twins has improved
significantly since data from cases followed in the 90's reported an
8-fold greater risk of cerebral palsy (CP) in MC twins over DC twins,
with this being 19-fold higher in MC twins with discordant growth
(Adegbite et al AJOG 2004,190:156-63). A 37\% rate of neurological
damage has been reported even in the normally grown twin of an sFGR
pair, when the co-twin has abnormal Dopplers; however, this was based on
neuro-imaging findings within the first month and a half of life
(Gratacos et al Ultrasound Obstet Gynecol 2004;24: 15-63). More recent
data has shown a difference in mild neurological morbidities only, but
follow-up, at a median of 24 months, ranged broadly from 12 months to 7
years (Rustico et al Ultrasound Obstet Gynecol 2017,49, 387-93). Despite
the limitations of the available outcome data, such information
underpins counselling in MC gestations complicated by sFGR. The question
``will my twins be OK in the end?'' remains one that is not easy to
answer with confidence.

The EPIPAGE2 cohort has the advantage of representing a more recent
large national cohort of preterm births, recruited over a single year
and with long term follow-up data. The sub-analysis presented here
(Horau et al BJOG 2023, TBC), addresses the association of chorionicity
and neurodevelopmental outcomes of prematurely delivered twins (22-34
weeks) at early school age (5 \selectlanguage{ngerman}½ years). The comprehensive testing likely
paints a more realistic picture of the neurodevelopmental and
neurobehavioural status of MC twins than these prior studies.

Within the described population, 24\% of twins were MC. The 20\% of
these complicated by TTTS were excluded from the outcome analysis given
the known impact of TTTS. Growth discordance of 20\% or more was found
in 26.2\% of the MC twins compared with 11.8\% of the DC twins. In the
context of a population with over a quarter of MC twins displaying
significant growth discordance, the results are encouraging. Although
fewer (68\%) of MC twins were alive at discharge compared to DC twins
(78\%), the severe CP rates at 5 years were equivalent at around 1\%.
Amongst survivors there were no differences in the neuro-developmental
or neuro-behavioural assessments between the MC and DC twins; with
adverse outcomes seemingly therefore being linked principally to
prematurity rather than chorionicity or growth discordance itself.

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