Outcome of early first-trimester pregnancies (< 6.1 weeks) with slow embryonic heart rate

The purpose of this article is to assess prospectively the value of concordant versus discordant gestational age (GA) calculations in predicting subsequent embryonic demise in embryos with a slow heart rate, as determined on early first-trimester ultrasound.

Thirty-six consecutive singleton pregnancies with slow embryonic heart rate (< 100 beats/min) measured on a 5.0- to 6.1-week ultrasound were prospectively identified. Pregnancies were defined as "discordant" if there was more than 5 days' difference between GA determined by biometrics compared with GA determined by last menstrual period and were defined as "concordant" if there was less than 5 days' difference between the GA measurements.

Of the 36 embryos with heart rate less than 100 beats/min at 5.0-6.1 weeks' GA, 16 went on to demise and 20 survived. Of the 16 that went on to demise, 14 were discordant (88%) and two were concordant (12%). Of the 20 that survived, 16 were concordant (80%) and four were discordant (20%). The proportion of discordant pregnancies that went on to demise was 14 of 18 (negative predictive value, 78%). The proportion of concordant pregnancies that went on to survival was 16 of 18 (positive predictive value, 89%). The rate of demise in the discordant group was significantly higher than that in the concordant group (p < 0.001, Fisher's exact test).

Embryonic heart rate less than 100 beats/min detected at 6.1 weeks or less is not necessarily a poor prognostic indicator. The likelihood of subsequent first-trimester survival is significantly higher if there is concordance between GA as calculated by biometrics and last menstrual period than if there is discordance.