4.4 Strengths and limitations
The main strength of our study lies in the following points. The first
one is that only healthy uncomplicated twin pregnancies were included.
Secondly, our reference charts were based on longitudinal data as well
adequate sample size, which made it available to develop growth centiles
to identify patterns and differences in fetal growth at different
gestational ages14. Thirdly, taking both chorionicity
and mode of conception into account promised our growth reference chart
a more reliable and sensitive tool in identifying growth restriction in
twins. Forth, the GAMLSS model has unique advantages in fitting the
changing curve over time, which has been applied by WHO to establish
child growth standards10. Moreover, making comparison
with data from singleton provided evidence to confirm that twin has
intrinsic growth pattern, emphasizing the importance of this study.
However, several weaknesses also warrant acknowledgement. First, this
study was a single-center design, there might be a selection bias.
However, International Peace Maternity & Child Health Hospital is the
top quality maternal and child health hospital in Shanghai, which
attracts pregnant women all around Shanghai. The hospital has opened
twin pregnancy clinic since 2015, which is one of three
specialist consultation settings for twin pregnancy in Shanghai.
Therefore, the twin pregnant women recruited through four years should
have a certain representative in Shanghai area. Secondly, very minority
(n=23) was MCDA twins conceived by ART, therefore, they were not
included in this study. Finally, although we adopted strict inclusion
criteria to acquire qualified target population, other high-risk
individual with unclear adverse perinatal outcomes was possible.