Crown-rump length measurements revisited.
UNLABELLED: Clinical and ultrasound data of 403 first-trimester pregnancies were collected prospectively. For our CRL study, two groups of patients were selected: Group A with an optimal (menstrual) history (111 patients, 156 CRL measurements) and Group B with available BBT charts (17 patients, 27 CRL measurements). Compared to the Robinson CRL curve (SD +/- 4.7 days) the curve of group A (SD +/- 4.4 days) showed a small underestimation of gestational age of 2.5 days in the 8th week, gradually declining (p less than 0.001). The CRL curve of group B (SD 4.3 days) is parallel to the group A curve, displaced 2.9 days to the left, and did not differ significantly from the Robinson curve. IN CONCLUSION: in contrast to suggestions in literature there is no need to revise the original CRL curve of Robinson. For individual variations in CRL measurements not only measure errors but also variations in the time of implantation and/or start of growth are responsible.