First-trimester screening in pregnancies conceived by assisted reproductive technology: significance of gestational dating by oocyte retrieval or sonographic measurement of crown-rump length.

OBJECTIVES

To evaluate, in pregnancies conceived by assisted reproductive technology, whether determination of gestational age (GA) by date of oocyte aspiration (DOA) or crown-rump length (CRL) at first-trimester screening influences the distribution of serum and sonographic markers or the performance of first-trimester screening for chromosomal abnormalities.

METHODS

GA was calculated using either DOA or CRL at blood sampling and nuchal translucency thickness (NT) measurement in 729 singleton pregnancies conceived by in-vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). Weight-corrected log multiples of the median (MoM) marker distributions specific for IVF pregnancy were established using multiple log regression and compared for DOA- and CRL-based GA calculation.

RESULTS

GA determined by CRL was significantly larger, albeit slightly, than was GA determined by DOA, with a mean difference of 1.50 (SD, 2.4) days (P < 0.001). Log MoM distributions of free beta-human chorionic gonadotropin and NT showed that GA dating by CRL resulted in significantly higher, albeit slightly, mean log MoM values compared with DOA dating. The reverse was the case for mean log MoM pregnancy-associated plasma protein-A. The SDs were similar for CRL and DOA dating. According to Monte Carlo simulation, the use of DOA or CRL for GA dating did not appreciably influence the performance of first-trimester screening.

CONCLUSIONS

DOA and CRL are practically equivalent when calculating GA for first-trimester screening. The correct method of GA dating for other purposes (e.g. estimated time of delivery) in IVF/ICSI pregnancies is still unresolved.