Comparison of actual and ultrasound estimated second trimester gestational length in in-vitro fertilized pregnancies

Objective. To compare actual and calculated gestational age in pregnancies conceived by in-vitro fertilisation. Methods. In 36 healthy women conceiving by in-vitro fertilisation an equation described for use in a Nordic population was used for calculating gestational age from the biparietal diameter and femur length at a routine 18-19 week scan. This was compared to actual gestational length estimated from the day between oocyte retrieval and embryo transfer. Results. The mean difference amounted to -0.86 days with a standard deviation of 2.86 days, a range of -5 to +6 days and a 95% confidence interval -0.11 to 1.83 (t=1.806, df = 35, p = 0.8). Correlation between the two methods was highly significant. Conclusion. The equation used allows prediction of term with sufficient accuracy for general use in our population.