Obstetric dating and assessment
Objective: To determine whether prior knowledge of obstetric estimate of gestational age creates a bias in assignment of gestational age by the Ballard assessment score. One examiner determined the best obstetric estimate of gestational age from the mother's chart (based on last menstrual period and earliest ultrasound) before assigning the score.Methods: The Ballard assessment score was done on 82 infants weighing less than 2500 g by two examiners, one who had prior knowledge of best obstetric gestational age estimate and the other who was masked to that information. The other examiner was masked to obstetric gestational age estimates.
Keep in mind that this is 6 to 11 weeks from the first day of the last menstrual period.
This study had over 99% power to detect a 1-week difference between the accuracy of masked and unmasked scores. Infants who weighed less than 2500 g were enrolled in the study. Statistics were analyzed by Spearman rank correlation test, plotting the measurement means against measurement differences, = 0.85), providing internal validation of Ballard scores.
Conclusion: Prior knowledge of obstetric gestational age did not bias the Ballard assessment score. Between January 1, 1998 and April 30, 1998, 82 infants who weighed less than 2500 g were enrolled in the study.
This examination is particularly helpful if you are unsure of you last menstrual period and will give you an accurate assessment of the age of the pregnancy and expected date of delivery.
The amount of anatomical information that can be gained from the scan is dependent on baby's age.