First-Trimester Crown-Rump Length and Risk of Chromosomal Aberrations—A Systematic Review and Meta-analysis

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Lower than expected first-trimester crown-rump length (CRL) is a common sonographic finding, usually leading to reassessment of gestational age.


The aim of this study was to perform a meta-analysis defining the risk of chromosomal aberrations in pregnancies with decreased first-trimester CRL.

Evidence Acquisition

A search was conducted by a research librarian in 5 databases, with no time or language restrictions. Original researches examining the risk of chromosomal aberrations in pregnancies with low CRL were selected. The effect estimates were presented as odds ratios with 95% confidence intervals).


Following screening of 3894 references, 12 articles were selected. Only 2 articles directly fulfilled the review goals, comparing the rates of chromosomal aberrations in small-CRL versus normal-CRL fetuses. Combined analysis of these 2 studies, encompassing a total of 403 fetuses with small CRL and 4047 control pregnancies, yielded an odds ratio of 5.54 (95% confidence interval, 1.2–26.1) for abnormal karyotype in small-CRL fetuses. Ten studies compared CRL in fetuses with specific chromosomal aberrations to pregnancies with normal karyotype, yielding a significant growth delay in fetuses with trisomy 18 (6 of 7 articles) and triploidy, but not in fetuses with trisomy 21. Overall quality of evidence was rated as “very low” using Grading of Recommendations Assessment, Development and Evaluation criteria.

Conclusions and Relevance

Our review results indicate that low first-trimester CRL might be associated with a significantly increased risk of chromosomal anomalies. Thus, invasive prenatal testing or cell-free DNA screening might be offered in such pregnancies, particularly if dating is certain.

Target Audience

Obstetricians and gynecologists, family physicians.

Learning Objectives

After completing this activity, the learner should be better able to describe the paucity of existing literature examining the risk of chromosomal aberrations in pregnancies with decreased first-trimester CRL, discuss the questionability of routine recommendation for gestational age correction in such pregnancies, and recall the appropriate management of such cases, including frequent sonographic fetal growth follow-up and detailed scan for sonographic anomalies, with possible consideration of invasive prenatal testing.

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