A prospective longitudinal study of growth velocity in twin pregnancy

Objectives fundamental research into the growth of twins is lacking. Twin g rowth in utero is commonly assumed to follow similar patterns of growth as that of singletons. This preliminary descriptive study on twin pregnancy ai med to define growth velocity as gestation advances, and to study if twin o rder, fetal sex, zygosity and chorionicity have any relationship to growth velocity. Methods One hundred and sixty-two women with twin pregnancies had an ultras ound examination at fortnightly intervals from 16 weeks until delivery. Fet al measurements of biparietal diameter, abdominal circumference and femur l ength were performed at each examination. Growth velocity for each paramete r was defined as the difference in measurements for that parameter divided by the time interval between measurements. Postnatally, zygosity and chorio nicity were determined by genetic fingerprinting and inspection of the plac enta, respectively. Results Growth velocity for all parameters decreased as gestation advanced, with the downward trend more noticeable after 32 weeks. Maximum and minimu m growth occurred at 22-23 weeks and 36-37 weeks, respectively. Maximum and minimum growth velocities for the abdominal circumference were 1.7 and 0.8 cm/week, respectively. Birth order, fetal sex, chorionicity and zygosity w ere not related to growth velocity. Conclusions These preliminary results suggest that growth velocity in twins decreases after 32 weeks' gestation. It appears that growth velocity is in dependent of birth order, fetal sex, chorionicity and zygosity.