A r etr ospecti ve l ongi tudi nal study w as per for med to quanti fy foetal gr ow th vel oci ti es i n tw i n pr egnanci es and to deter mi ne the effect of var i abl es speci fi c to tw i n pr egnanci es on gr ow th vel oci ty. Foetal gr ow th vel oci ty standar d devi ati on (Z) scor es w er e cal cul ated fr om ser i al ul tr asound data usi ng publ i shed si ngl eton r efer ence data for 131 consecuti ve sets of tw i ns fr om 30 to 37 w eek s' gestati on. Compar ed w i th l ow -r i sk pr egnanci es, the tw i n foetal abdomi nal ar ea gr ow th vel oci ty Z scor es w er e si gni fi cantl y r educed fr om 30 to 37 w eek s and bi par i etal di ameter gr ow th vel oci ty Z scor es w er e al so si gni fi cantl y l ow er, fr om 30 to 33 w eek s. A mongst the tw i n pai r s ther e w er e no si gni fi cant di ffer ences i n Z scor es w i th r espect to chor i oni ci ty, foetal sex, bi r th or der to w hether del i ver y w as pr ematur e or ter m. Thi s r etr ospecti ve study has demonstr ated that tw i n foetal gr ow th vel oci ty i s r educed w hen compar ed to si ngl etons fr om at l east as ear l y as 30 w eek s' gestati on. Tw i n speci fi c var i abl es such as chor i oni ci ty, sex, bi r th or der and subsequent pr ematur e bi r th do not need to be accounted for i n the i nter pr etati on of gr ow th vel oci ti es i n tw i ns. The cl i ni cal i mpor tance of deter mi ni ng foetal gr ow th vel oci ty i n tw i n pr egnanci es aw ai ts fur ther pr ospecti ve study.Keyw or ds: foetal grow th vel oci ty, tw i ns, chori oni ci ty, foetal sex, bi rth order, preterm and term delivery

A r etr ospecti ve l ongi tudi nal study w as per for med to quanti fy foetal gr ow th vel oci ti es i n tw i n pr egnanci es and to deter mi ne the effect of var i abl es speci fi c to tw i n pr egnanci es on gr ow th vel oci ty. Foetal gr ow th vel oci ty standar d devi ati on (Z) scor es w er e cal cul ated fr om ser i al ul tr asound data usi ng publ i shed si ngl eton r efer ence data for 131 consecuti ve sets of tw i ns fr om 30 to 37 w eek s' gestati on. Compar ed w i th l ow -r i sk pr egnanci es, the tw i n foetal abdomi nal ar ea gr ow th vel oci ty Z scor es w er e si gni fi cantl y r educed fr om 30 to 37 w eek s and bi par i etal di ameter gr ow th vel oci ty Z scor es w er e al so si gni fi cantl y l ow er, fr om 30 to 33 w eek s. A mongst the tw i n pai r s ther e w er e no si gni fi cant di ffer ences i n Z scor es w i th r espect to chor i oni ci ty, foetal sex, bi r th or der to w hether del i ver y w as pr ematur e or ter m. Thi s r etr ospecti ve study has demonstr ated that tw i n foetal gr ow th vel oci ty i s r educed w hen compar ed to si ngl etons fr om at l east as ear l y as 30 w eek s' gestati on. Tw i n speci fi c var i abl es such as chor i oni ci ty, sex, bi r th or der and subsequent pr ematur e bi r th do not need to be accounted for i n the i nter pr etati on of gr ow th vel oci ti es i n tw i ns. The cl i ni cal i mpor tance of deter mi ni ng foetal gr ow th vel oci ty i n tw i n pr egnanci es aw ai ts fur ther pr ospecti ve study.Keyw or ds: foetal grow th vel oci ty, tw i ns, chori oni ci ty, foetal sex, bi rth order, preterm and term delivery