Fetal Crown–Chin Length to Crown–Rump Length Ratio as a Prenatal Sonographic Marker for Triploidy at First Trimester

Abstract

Objectives-To investigate the ratio of Crown to Chin length (CCL) to Crown-rump length (CRL) between triploid and normal fetuses at first trimester and establish a reference range of fetal CCL/CRL ratio.Methods-Three hundred and twenty-five normal and 12 triploid fetuses were reviewed in this study. The image of fetal Crown-rump length (CRL) was acquired retrospectively. CCL and CRL were measured offline by two experienced sonographers, we obtained each averaged value of CCL and CRL as the final data for analysis. A normal range of CCL was established and CCL/CRL ratio was analyzed in normal and triploid fetuses.Results-In 325 normal fetuses, CCL increased with gestational age following a linear trend from 20 mm at a CRL of 45-36 mm at a CRL of 84 mm (CCL (mm) = 3.65 + 0.38 CRL, R 2 = 0.821, P = .000). The CCL/CRL ratio decreased with gestational age from a mean of 0.46 at a CRL of 45 mm to 0.41 at a CRL of 84 mm (PML/CRL = 0.502-0.001 CRL, R 2 = 0.093, P = .000). All 12 triploid fetuses had a CCL/CRL ratio above the 95th percentile. When the 95th percentile are used as cutoff values, the detection rate, falsepositive rate, and the positive likelihood ratio are 100%, 5%, and 20, respectively.Conclusions-The present study demonstrates that fetal CCL/CRL ratio can be used and effective ultrasound marker in screening for triploidy during the first trimester.

The Application of Crown‐Chin Length to Crown‐Rump Length Ratio in Predicting Fetal Skeletal Dysplasia at First Trimester

“…Wang et al 12 suggested that the biparietal diameter/femur length (BPD/FL) ratio can predict thanatophoric dysplasia in the first trimester of pregnancy; it showed that the BPD/FL ratio increased in both 4 cases at first trimester and 20 cases at mid and third trimester. Recently, we reported 8 that the fetal CCL/CRL ratio increased significantly in triploid fetuses, which showed that the detection rate, false‐positive rate, and the positive likelihood ratio are 100, 5, and 20%. During the process of data review, we found that this ultrasound marker also increased in one fetus with skeletal dysplasia at 12 weeks of gestation, which showed short long bones, bowed femurs, omphalocele, and small thorax as well.…”

“…We have previously reported the normal range of fetal CCL/CRL ratio in 325 singleton pregnancies with chromosomally normal fetuses. 8 Normal ranges in this study were based on the 325 normal fetuses used in our previous publication 8 and 93 normal new cases for a total of 418 fetuses. CCCL and CRL measurements were performed in the normal population and compared to measurements in fetuses with skeletal dysplasia.…”

“…In our previous study, 8 the fetal crown‐chin length (CCL) to crown‐rump length (CRL) ratio was first applied in prediction of fetal triploidy. It showed that CCL/CRL ratio was significantly increased in triploid fetuses with a detection rate, false‐positive rate, and the positive likelihood ratio are 100, 5, and 20%, respectively.…”