Ultrasonographic markers for chromosomal abnormalities in women with negative nuchal translucency and second trimester maternal serum biochemistry

Objective To analyze the value of second trimester ultrasound examination a mong those women whose fetuses were indicated 50 be at low risk of chromoso mal anomalies on the basis of both first trimester nuchal translucency meas urement and second trimester biochemical screening. Methods A retrospective study of 5500 pregnancies carried out at the fetal medicine unit, Royal Free Hospital. During a period of over 3 years 5500 pr egnancies under went a first trimester scan and nuchal translucency measure ment which enabled the detection of 62% (20 of 32) of all chromosomal anoma lies. From the remaining pregnancies that underwent second trimester bioche mical screening, 3548 were considered negative (risk < 1 : 250; using mater nal serum free beta human chorionic gonadotrophin and alpha fetoprotein). T he ultrasound markers that were examined were: shortened femur length, echo genic bowel, pyelectasis, choroid plexus cysts and echogenic intracardiac f oci. The likelihood ratios for chromosomal aneuploides for each of these ma rkers were calculated. Results Of the 3548 screen negative pregnancies, 3541 (99.8%) had a normal karyotype. Seven (0.2%) fetuses had an abnormal karyotype including four (0 .11%) with trisomy 21, one with trisomy 18 and two with 47XXY. Second trime ster ultrasound markers were found in two of the five (40%) with severe chr omosomal anomalies compared to 184 of 3541 (5.2%) with normal karyotypes. D etection of one or more ultrasound markers in a screen negative Pregnancy i ncreased the possibility of chromosomal aneuploidy and a negative ultrasoun d decreased the risk by a likelihood ratio of 0.6 (95% confidence interval, 0.3-1.3). The risk was considerably increased when two or more markers wer e detected and we would recommend karyotyping under these circumstances. Conclusion This Preliminary data indicates a possible role for abnormal ult rasound markers in assessing the risk of chromosomal abnormalities in patie nts considered to be at low risk by nuchal translucency and serum screening . However analysis of a much larger study group will have to be conducted 5 0 assess the significance of individual markers.