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Identification of early pregnancy landmarks by transvaginal sonography: analysis by logistic regression
M P Steinkampf1, D S Guzick, K R Hammond
1Department of Obstetrics and Gynecology, University of Alabama at Birmingham 35233-7333, USA.
Objective:
To assess the feasibility of logistic regression analysis for determining the gestational ages at which detection of early pregnancy landmarks first can be observed.
Design:
Retrospective analysis.
Setting:
University-based tertiary care clinic.
Patient(S):
Eighty-two women with viable singleton pregnancies in whom ovulation had been achieved by an injection of hCG.
Intervention(S):
Two hundred fifteen transvaginal sonographic scans.
Main Outcome Measure(S):
Logistic regression was used to estimate the probability of detection of sonographic findings as a function of gestational age.
Result(S):
We found that the likelihood of visualization of a gestational sac or fetal heart motion could be represented accurately by logistic equations. Gestational age at which there was 95% probability of visualization was 35.5 days for the gestational sac and 44.5 days for fetal cardiac activity. The probability of detecting fetal cardiac activity was 95% when the mean gestational sac diameter was 1.6 cm and was 99% at 1.9 cm.
Conclusion(S):
The sonographic appearances of developmental landmarks in early pregnancy occurs within well-defined gestational time periods, and the probabilities for visualization can be closely approximated using a logistic model. Our results suggest that the number of sonographic examinations required to document infertility treatment success can be minimized by surveillance at standardized gestational ages.