Can a smaller than expected crown-rump length reliably predict the occurrence of subsequent miscarriage in a viable first trimester pregnancy?

ABSTRACT

AIM: To elicit the diagnostic value of smaller than expected crown-rump length (CRL) to predict the occurrence of subsequent miscarriage in women with a viable first trimester pregnancy. METHODS: A cohort study was conducted in the fetal special care unit of a tertiary care maternity hospital. The recruited participants were young pregnant women at 6-13 weeks of gestation. Transvaginal ultrasonography was performed to determine pregnancy viability and measure the embryonic CRL. To compare the differences in CRL between those pregnancies that remained viable and those that subsequently miscarried, the deviation of observed and expected CRL was calculated and expressed in standard deviations (SD) as Z score. The primary outcome measure was the percentage of pregnancies with antecedent growth delay that miscarried by the end of the first trimester. RESULTS: Of the pregnancies that subsequently miscarried, 79.3% (42/53) had smaller than expected CRL, and in 56.6% (30/53) the CRL was 2 SD or less from that expected for gestational age (GA). The mean Z score for CRL was significantly lower in pregnancies that subsequently miscarried compared to pregnancies that remained viable (-2.9 ± 2.6 vs -0.8 ± 2.1, respectively, P < 0.001). A CRL of 2 SD or less from that expected for GA as a cut-off point had a sensitivity of 56.6, specificity of 81.9, positive predictive value of 36.6, negative predictive value of 91.1, likelihood ratio positive of 3.1 and likelihood ratio negative of 0.5 in predicting subsequent miscarriage. CONCLUSION: Viable first trimester pregnancies with small for GA CRL were associated with a higher probability of a subsequent miscarriage.