Adverse perinatal outcomes associated with crown-rump length discrepancy in in vitro fertilization pregnancies.

Objective(s): To determine whether an association exists between small crown-rump length (CRL) and adverse obstetrical outcomes in pregnancies conceived by IVF and to compare a CRL reference based on IVF pregnancies to a reference based on spontaneous pregnancies.

Design: Retrospective cohort study. CRL was classified as small by comparing it with the local university hospital maternal fetal medicine standard and the Monash IVF reference chart.

Setting: University-affiliated fertility center.

Patient(s): Singleton pregnancies conceived by IVF with ultrasounds performed between 7+0 and 8+6 weeks of gestational age.

Intervention(s): None.

Main Outcome Measure(s): Pregnancy loss, preterm birth, and low birth weight.

Result(s): Included were 940 clinical pregnancies. The overall and CRL-discrepant miscarriage rates were 12.7% and 41%, respectively. When CRL was small, the maternal age-adjusted odds of miscarriage were 13.8 times higher (95% confidence interval [CI], 8.9-21.6). At age 30, small CRL was associated with a 30% risk of miscarriage, versus 61% at age 45. There was no association between small CRL and preterm birth or low birth weight. The sensitivity and specificity for predicting miscarriage from the optimal Monash cut point were 0.69 (95% CI, 0.61-0.77) and 0.84 (95% CI, 0.82-0.87), which were similar to those of the CRL reference based on spontaneous pregnancies.

Conclusion(s): Small CRL in IVF pregnancy was strongly associated with miscarriage, especially in the context of advanced maternal age. Small CRL was not associated with preterm birth or low birth weight. A CRL reference based on IVF pregnancies was equivalent to the standard reference for predicting miscarriage.