(Invited Mini-Commentary on Marleen et al. BJOG-20-0566.R2)
C Andrew Combs MD, PhD
The Mednax Center for Research, Education, Quality, and Safety, Sunrise,
Florida, USA
Obstetrix Medical Group, San Jose, California, USA
Correspondence:
C Andrew Combs
Mail: 900 E Hamilton Av, Campbell, CA, USA 95008
Mobile telephone: +1-408-314-1792
E-mail: andrewcombs@me.com
Tweetable abstract: Identical twin pregnancies have more preterm births
and other complications than fraternal twin pregnancies.
Mini-Commentary
A decade ago, Professor Kypros Nicolaides of Kings’ College opined,
“There is NO diagnosis of twins. There are only monochorionic or
dichorionic twins. This diagnosis should be written in capital red
letters across the top of the patient’s chart.” (Quoted by Moise and
Johnson, Am J Obstet Gynecol 2010; 203:1-2.) To make this diagnosis, it
is essential to establish chorionicity as early as possible in every
twin pregnancy.
Monochorionic twin pregnancies have long been known to have higher rates
of miscarriage, congenital anomalies, stillbirth, and neonatal death
than dichorionic twin pregnancies. Intertwin vascular anastomoses are
present in most monochorionic twin placentas, leading to complications
such as twin-twin transfusion syndrome (TTTS), twin anemia-polycythemia
sequence (TAPS), twin reversed arterial perfusion (TRAP) sequence, and
unequal placental sharing (UPS).
Monochorionic twins require intensive antenatal surveillance. Because of
the increased risk of congenital anomalies, fetal echocardiogram is
recommended in addition to routine ultrasound fetal anatomy survey.
Because of the risk of TTTS, TAPS, TRAP and UPS, sonographic
surveillance is recommended every 2 weeks starting at 16 weeks of
gestation. Because of the risk of stillbirth, serial antenatal
cardiotocography is recommended. Scheduled delivery is recommended
earlier for monochorionic twins than for dichorionic twins (NICE
Guideline 137, 2019; ACOG, Obstet Gynecol 2019;133:e151-5; Cheong-See et
al, BMJ 2016;354:i4353).
Regardless of chorionicity, 60% of twins are born preterm, resulting in
substantial perinatal morbidity and mortality. Prevention of preterm
birth (PTB) is a major priority for management of twin pregnancy.
The systematic review by Marleen and colleagues is the first of several
studies planned by the authors to evaluate risk factors for PTB in twin
pregnancy. Prior reports have suggested that monochorionic twins have
higher rates of PTB than dichorionic twins but, as the authors note,
there has been no prior systematic review of this association. It is not
surprising that the review shows an increased overall rate of PTB among
monochorionic twins in all gestational age ranges, given that
complications such as stillbirth, TTTS, TAPS, TRAP, and UPS often result
in iatrogenic PTB. Indeed, iatrogenic PTB before 37 weeks of gestation
should be routine for monochorionic twins because of the increasing risk
of stillbirth past 36+6 weeks cited in the current
NICE Guidelines (2019, op. cit .). However, Marleen and colleagues
also report that spontaneous PTB at <37 weeks and ≤34
weeks is increased in monochorionic twin pregnancy, which cannot be
directly explained by monochorionic placental complications.
The overarching goal of Marleen and colleagues is to develop tools to
predict which twin pregnancies are at risk of PTB so that preventive
measures can be taken. Unfortunately, it is not currently known what
preventive measures will reduce the high risk of early spontaneous PTB
among monochorionic twin pregnancies. Prophylactic bedrest,
hospitalization, uterine activity monitoring, tocolysis, cerclage,
cervical pessary, and progestogens have not proven effective for
unselected twin pregnancies. Future research will be needed to determine
the value of such interventions for women with twin pregnancy plus
additional risk factors such as a short cervix, prior PTB, or
monochorionicity.
Acknowledgements: None
Disclosure of Interests: C Andrew Combs declares “No
relevant or competing interests”
Contribution to Authorship: CAC did 100% of the
planning, writing, and submission.
Details of Ethics Approval : Not applicable
Funding: None
References: Cited in-line per instructions for
Mini-Commentary
Tables/Figures: None