Objective: The goal of this study was to determine the accuracy of an everyday practice for assessing gestational age by ultrasound and redefine the correction of gestational age policy.
Materials and methods: This study used first trimester measurements taken during a three-year period. We considered all births from pregnancies that began by an in vitro fertilization procedure. We examined 143 consecutive files containing 257 measurements made by 72 different operators. We applied two reference curves to calculate the date the pregnancy began and the centiles of the prediction interval for +/- 7, +/- 5 and +/- 3 days.
Results: The prediction intervals for +/-7, +/-5, +/-3 days excluded 2%, 6%, and 25% respectively of the embryos from one of the two reference curves. These intervals were 1%, 5% and 20%, were better for the other curve.
Conclusion: Correction of gestational age has to take into consideration variations in the embryo length. We correct the gestational age only if the difference with ultrasound assessment is more than one week.