Uterine height and umbilical perimeter curves in twin pregnancies.

From previous research, which gave standard curves for the evolution of uterine height and umbilical perimeter according to gestational age in the case of single pregnancies, the authors propose curves which show the variations of these two parameters in twin pregnancies. The observed differences are sufficient to allow a diagnosis of twin pregnancy as soon as the 18th week of amenorrhea. This observation is interesting because, until now, a systematic early B-scan examination has not been performed as a rule.