Relationship between crown-rump length and early detection of cardiac activity

To investigate whether improvements in sonographic technology would allow detection of embryonic demise at a crown-rump length (CRL) < 5 mm.

A prospectively collected, computerized ultrasound database was queried for singleton gestations with CRL < or = 5 mm from January 2000 to February 2003. Embryonic viability was determined by repeat ultrasound examination after 6 weeks'gestation confirming cardiac activity or by documentation of an ongoing pregnancy. Viability rates in the presence or absence of cardiac activity were calculated for CRL of 2.0-2.9, 3.0-3.4, 3.5-3.9, 4.0-4.4, 4.5-4.9 and 5.0 mm. Sensitivity, specificity, positive predictive value and negative predictive value for embryonic demise were calculated, with a subanalysis based on the presence of vaginal bleeding.

Outcome was available for 179 of 195 gestations meeting inclusion criteria. The absence of cardiac activity at CRL > or = 3.5 mm had 100% positive predictive value and specificity. The presence of vaginal bleeding did not affect this cutoff.

Improved sonographic technology permits diagnosis of embryonic demise at a CRL > or = 3.5 mm under ideal conditions. Vaginal bleeding increases the likelihood of demise, but does not alter test performance. Further investigation is warranted, as our data suggest a limit closer to 3 mm.