4.3 Clinical implications
The accuracy of intrauterine growth assessment for twins depends on the
establishment of twin-specific growth charts, and the longitudinal
ultrasonographic standards have benefits in recognizing growth pattern
variations at different gestational ages31. The
international society of obstetrics and gynecology ultrasound emphasized
the clinical significance of development and use of twin-specific growth
charts when assessing fetal growth of twins since
201632. In medical practice, it has been well-known
that growth restriction in twins is prevalent due to the slower growth
rate in the third trimester5-8. In our study, all the
median (50th percentile) biometric parameters of SC-MCDA, SC-DCDA,
ART-DCDA twins were lower at each gestational week compared with fetal
biometry reference of Chinese singleton33, 34.
Therefore, over-diagnosis of restricted intrauterine growth should be a
common concern when adopting the diagnostic criteria based upon the
standard of singletons. For a long time,
although there are the continuous efforts, trying to establish fetal
growth curve for twins, but the issue has not been resolved. The
existing data has inherent limitations, for example, some of the data
came from birth weight and cannot be applied to the growth and
development assessment during pregnancy24, 35-38, some
others recruited subjects by small sample size5, 11,
15 or without exclusion of high-risk pregnancy5, 12,
16. In the present study, we got over the limitations and largely
promised our growth reference chart customized for chorionicity and mode
of conception a more reliable tool to distinguish cases with fetal
growth restriction in twins39.
We are aware that downgrading the fetal growth reference may sacrifice
the sensitivity to identify pathological fetal growth restriction. Our
subject enrollment strategy adopted strict inclusion criteria for
pregnant woman, which ensured a qualified sensitivity in the early
screening of fetal growth restriction. Notably, our sampled population
included pregnancies via ART. Since twin pregnancies via ART accounts
for more than half of twins, our growth charts customized for conception
mode would be more generalizable to the current population of twins in
China. The results of this study illustrated an asymmetric pattern of
growth velocity between DCDA and MCDA twins, which has been confirmed by
previous studies 6, 11, 16. In addition, it has been
suggested that chorionicity has a significant independent effect on
birthweight40, and the threshold of physiological
intertwin size discordance of fetal biometry also vary according to the
chorionicity41. In this case, developing
growth reference charts customized
for chorionicity is necessary.
In this study, six fetal biometric measurements obtained from ultrasound
were opted to customize the growth reference, but not only the EFW. A
previous study found that some biometric measurements may vary according
to parental ethnicity or different constitutional characteristics, not
all the differences can be specifically explained by the changes of
EFW6. As proposed by previous
studies42, 43, we developed all fetal biometric
parameters growth charts rather than only EFW in most
studies8, 12, 13. The full-spectrum parameters could
enrich our knowledge on fetal changes in uterus, which should be
clinically significant to promote
a more comprehensive evaluation of fetal intrauterine growth.