Influence of medically assisted reproduction techniques on crown-rump length and biochemical markers of trisomy 21 in the first trimester of pregnancy.

Objective: To determine whether there is a difference between the known gestational age in pregnancies conceived after IVF and the estimated gestational age based on the crown-rump length (CRL) measurement during the first trimester.

Design: We retrospectively (between 2007 and 2012) studied a cohort of 6,739 patients who underwent ultrasonography between 11 and 13+6 weeks of amenorrhea.

Setting: Hospital.

Patient(s): Group A consisted of 6,621 patients with regular menses whose term was calculated based on the date of their last menstrual period (LMP). Group B consisted of 529 patients whose pregnancies had been achieved by IVF and in whom term was calculated based on the date of fresh or frozen ET.

Intervention(s): None.

Main Outcome Measure(s): The gestational age difference was obtained by comparing the age obtained by measuring the CRL (Robinson's curve) with the gestational age calculated in accordance with LMP in group A or with ET day in group B.

Result(s): The gestational age difference was significantly more in group B (2.3 days vs. 0.84 days in group A). We found a significant difference regarding biochemical markers for trisomy 21 to the detriment of group B with a significantly reduced pregnancy-associated protein P-A multiple of median (0.78 vs. 0.92).

Conclusion(s): There appears to be a small difference in CRL development between spontaneous pregnancies and pregnancies conceived by assisted reproductive technology (ART). Specific ultrasonographic curves for pregnancies conceived by ART would be more relevant and precise. The underlying pathophysiological mechanisms are not very clear and offer possibilities for future research.