DNA concentrations in amniotic fluid according to gestational age and fetal sex: data from 2573 samples

In some cases of prenatal genetic testing, an ample amount of fetal DNA is needed, to allow for parallel testing (conducting several genetic tests simultaneously). This study investigated the association between amniotic fluid DNA concentration and various factors. We aimed to define the required amount of amniotic fluid to be extracted in amniocentesis, to allow parallel testing throughout gestational weeks.

DNA concentration was analyzed from amniocentesis samples taken during the years 2016-2022. Sex association was also analyzed in postnatal whole blood samples from a separate cohort. Theoretical minimum volume of amniotic fluid needed to ensure enough DNA for chromosomal microarray analysis and exome sequencing was calculated.

We focused our analysis on 2573 samples, which were taken during weeks 17-23 and 30-35. DNA concentrations increased from weeks 17 to 21, with relatively stable concentrations thereafter. Significantly higher DNA concentrations were seen in pregnancies of female fetuses. DNA concentrations in postnatal whole blood samples did not show this association. Across most weeks, the volume needed to extract 2 µg of DNA from 95% of the samples was about 34 ml.

DNA concentrations in amniotic fluid vary according to gestational age and are higher in pregnancies of female fetuses. This should be considered when determining the volume of fluid extracted and the timing of amniocentesis, with greater volumes needed in earlier stages of pregnancy.