Development of fetal growth charts in twins stratified by chorionicity and mode of conception:a retrospective cohort study in China

Background:Twin pregnancies continue to increase worldwide;however,the current clinical prenatal evaluation for the intrauterine growth of twins still relies on the growth standards of singletons.We attempted to establish a set of fetal biometric references for Chinese twin pregnancies,stratified by chorionicity and conception mode as spontaneously conceived monochorionic diamniotic(SC-MCDA),spontaneously conceived dichorionic diamniotic(SC-DCDA),and assisted reproductive technology dichorionic diamniotic(ART-DCDA)twins.Methods:From 2016 to 2019,the ultrasonographic fetal biometric measurements were longitudinally collected in pregnant women,including fetal weight,biparietal diameter,head circumference,abdominal circumference,femur length,and humerus length.The linear mixed models were used to test the difference of growth patterns between groups,and the growth curve of each biometric parameter was modeled by a generalized additive model for location scale and shape.Results:A total of 929 twin pregnant women and 2019 singleton pregnant women,met the inclusion criteria.Among twin pregnancies,148 were SC-MCDA,215 were SC-DCDA,and 566 were ART-DCDA twins.Overall,SC-DCDA twins grew faster than SC-MCDA twins,while slower than ART-DCDA twins(all P<0.05),and all of the three groups showed significant differences comparing with singletons,especially during the third trimester.Hence,the customized fetal growth charts of each fetal biometric parameter were,respectively,constructed for SC-MCDA,SC-DCDA,and ART-DCDA twins.Conclusions:The fetal biometric trajectories demonstrated characteristic patterns according to chorionicity and conception mode.To fill the gap,we modeled fetal biometric parameters for Chinese SC-MCDA,SC-DCDA,and ART-DCDA twin pregnancies,hoping to provide a reference for the further establishment of fetal growth reference values for Chinese twin fetuses.