Gestational age in pregnancies after in vitro fertilization: comparison between ultrasound measurement and actual age.

ABSTRACT

OBJECTIVE: To compare gestational age (GA) calculated from oocyte retrieval and from ultrasound measurements in pregnancies after in vitro fertilization (IVF). DESIGN: In a retrospective study of 253 women with singleton and 84 women with twin pregnancies conceived from IVF, GA calculated from the day of oocyte retrieval was compared with GA calculated in the second trimester of pregnancy from ultrasound measurements of biparietal diameter (BPD) and femur length (FL). RESULTS: For singletons, the mean GA calculated from ultrasound measurements was significantly shorter than the mean GA estimated from the day of oocyte retrieval. The mean difference was 1.9 days (SD 3.3; 95% CI 1.5-2.4) if only BPD was used and 2.1 days (SD 2.1; 95% CI 1.6-2.5) if BPD and FL were combined. For twins, the mean GA calculated from ultrasound measurements was also significantly shorter than the mean GA calculated from the day of oocyte retrieval. The mean difference was 1.4 days (SD 2.7; 95% CI 1.0-1.8) if BPD was used and 1.6 days (SD 2.5; 95% CI 1.2-2.0) if BPD and FL were combined. CONCLUSIONS: In IVF pregnancies, term prediction using ultrasound in the second trimester is reliable and may reduce the number of pregnancies subsequently classified as post-term, thus avoiding unnecessary obstetric interventions.