Prenatal evaluation of genetic variants in fetuses with small head circumference: A single-center retrospective study.

• Small fetal HC that are less than −3 SD is associated with genetic variants, especially those with intracranial anomalies. • Fetuses with small head that do not reach the diagnosis criteria of microcephalycan't be simply explained as part of FGR. • Genetic variants, mainly CNV and SNV, can explain a substantial proportion of small fetal HC and most them are de novo. • CMA is practical for testing fetuses with small HC, and WES is more effective for genetic testing. • The novel findings about microcephaly-associated genes add value to the clinical use of exome sequencing in this population. • These findings help with the prenatal diagnosis of suspected fetal microcephaly and distribute to our clinical counselling. Objectives: To comprehensively evaluate the contributions of numerical chromosomal abnormality, copy number variant (CNV), and sequence variant (SV) to fetuses with small head circumference in a Chinese cohort using chromosome microarray analysis and whole exome sequencing. Methods: A total of 157 fetuses with small heads defined as head circumference < − 2 standard deviation (SD) were recruited between October 2014 and March 2023. We used the ultrasonic measurement parameter Z-score to define small head as possible microcephaly (3 < Z ≤ -2), microcephaly (-5 < Z ≤ -3), or pathologic microcephaly (Z ≤ -5). Ultrasound findings and genetic results were analyzed. Results: The overall diagnostic yield of chromosomal abnormalities by microarray analysis was 13 %. Whole exome sequencing revealed eight novel variants and two interesting candidate genes and provided a 25.4 % incremental yield compared with microarray analysis. Of the detected SVs, 56 % were de novo and the most common inheritance pattern was autosomal dominant inheritance presented in 11/16 fetuses. Compared with isolated small heads, non-isolated small heads had a significantly higher detection rate of chromosomal abnormalities (16 % vs. 3.0 %, P = 0.049) but not SVs (24 % vs. 5.5 %, P = 0.126). Subgroup analysis showed that intracranial anomalies had a similar high detection rate of SVs in fetuses with all small heads subgroups while no chromosomal abnormalities and causative SVs were found in fetuses with isolated possible microcephaly. Conclusions: Ultrasound findings of small fetal head circumference < 3 SD below the mean, especially those with intracranial structural abnormalities, indicate the need for genetic counseling. Genetic variants, mainly copy number variants and SV, may be responsible for the substantial proportion of small fetal head circumference, while most are de novo. Whole exome sequencing and microarray analysis are effective diagnostic approaches for this population. [ABSTRACT FROM AUTHOR]