1| INTRODUCTION
Complications of preterm birth (PTB) are the primary cause of death
among children in the first 5 years of life, accounting for
approximately 35% of deaths among new-borns and 18% of all paediatric
deaths.1 Twin gestations are increasing in number and
currently account for 3% of all live births and approximately 15-20%
of all PTBs.2 The incidence of PTB is 6-8 times higher
in twin pregnancy than in singleton pregnancy.3Approximately 70% of twins are born preterm due to preterm premature
rupture of membranes or spontaneous labour, while others result from an
iatrogenic delivery indicated by monochorionicity, preeclampsia or other
maternal or foetal disorders.4,5
Regarding preterm babies, longer gestational age at birth is associated
with better prognosis. The EPIPAGE-2 cohort study demonstrated that the
survival rates at 22-26, 27-31, and 32-34 weeks of gestation are 51.7%,
93.1%, and 98.6%, respectively.6 Compared with
singletons, twins born preterm (before 32 weeks of gestation) are at
twice the risk of high-grade intraventricular hemorrhage and
periventricular leucomalacia.7 Therefore, better
prediction, prevention, and management of PTB is necessary to improve
the quality of maternal and neonate care.
To date, strategies for the prevention of PTB in twin pregnancy, such as
the use of vaginal progesterone, a cervical pessary and a cervical
cerclage, remain controversial or are considered to have limited
effects.5, 8-14 To address the growing desire for
better guidance for clinical practice, it is a prerequisite to
distinguish the patients who are at an increased risk of extreme and
very-PTB among the whole twin-pregnancy population, as follow-up
treatment may be associated with greater benefit than workload in this
high-risk population.
As a demonstrably available and reproducible method, cervical assessment
with transvaginal ultrasonography has been increasingly
used.15-17 Cervical shortening and cervical funneling
are associated with a higher risk of preterm
delivery.18-24 However, the predictive accuracy of
cervical length for PTB in twin pregnancies are conflicting. Its
isolated use as a screening tool has limited value due to low
sensitivity.16, 25, 26 In addition, previous research
has demonstrated that the risk of PTB is also affected by maternal
demographic features, such as ethnic origin, age, primiparity,
chorionicity, prepregnancy body mass index (BMI) and history of previous
preterm delivery or late-term abortion.27-32In a sense, twin gestation itself is one of the strongest risk factors
for PTB.4,33 Assessment of the individual maternal
prognosis requires clinicians to consider an array of maternal
demographic factors and clinical variables that may be clinically
challenging to synthesize. However, the relative contribution of certain
characteristics to a given individual’s likelihood of preterm birth and
whether or how these features may interact remain poorly understood.
Thus, instead of complicating the clinicians’ lives with close
monitoring and administration resulting from an undefined or inherently
subjective risk assessment, it would be useful to invest our research
efforts in developing a simple and practical algorithm to calculate a
risk assessment of PTB for twin pregnancies, similar to the first
trimester genetic disease screening tools or the Framingham heart
disease score.34
The purpose of this study is to improve our collective understanding of
valuable predictive factors related to preterm birth of twin gestation.
We then used these factors to develop and validate the prediction model
of spontaneous PTB (SPTB) at <32 weeks to provide a
comprehensive risk estimation as a clinical assessment tool.