Foetal growth velocities in twin pregnancies.

A retrospective longitudinal study was performed to quantify foetal growth velocities in twin pregnancies and to determine the effect of variables specific to twin pregnancies on growth velocity. Foetal growth velocity standard deviation (Z) scores were calculated from serial ultrasound data using published singleton reference data for 131 consecutive sets of twins from 30 to 37 weeks' gestation. Compared with low-risk pregnancies, the twin foetal abdominal area growth velocity Z scores were significantly reduced from 30 to 37 weeks and biparietal diameter growth velocity Z scores were also significantly lower, from 30 to 33 weeks. Amongst the twin pairs there were no significant differences in Z scores with respect to chorionicity, foetal sex, birth order to whether delivery was premature or term. This retrospective study has demonstrated that twin foetal growth velocity is reduced when compared to singletons from at least as early as 30 weeks' gestation. Twin specific variables such as chorionicity, sex, birth order and subsequent premature birth do not need to be accounted for in the interpretation of growth velocities in twins. The clinical importance of determining foetal growth velocity in twin pregnancies awaits further prospective study.