Objective To assess the impact of non‐invasive prenatal testing (NIPT) on trends in the prenatal diagnosis of sex chromosome aneuploidy (SCA) in a population with >73,000 annual births. Method Retrospective population‐based cohort study from 1986–2016 of all women undergoing prenatal diagnosis before 25 weeks gestation in the Australian state of Victoria. Statistical significance was tested using the chi‐square test for trend or proportions. Results There were 2,043,345 births and 842 SCA diagnoses from 1986–2016. The percentage of prenatal diagnostic tests leading to a SCA diagnosis increased significantly from 0.95% in 2010 to 2.93% in 2016 (p < 0.001) but due to a concurrent decline in testing, the annual prenatal diagnosis rate of SCA remained stable at 4.4/10,000 births. Among confirmed fetal SCAs the most common indication for testing in 1986 was advanced maternal age (63%); in 2016 it was high risk NIPT (49%). Conclusion SCAs now make up an increasing proportion of prenatal diagnostic results but due to the overall decline in diagnostic testing, the prenatal prevalence as a percentage of births remained steady. The ascertainment of fetal SCA has evolved from an incidental finding after testing for increased risk of trisomy 21, to a diagnosis obtained after suspected SCA on NIPT.

is no data on fetal thymus size in pregnancies complicated by maternal diabetes. Therefore, the objective of our study was to evaluate the influence of maternal diabetes on fetal thymus size. Methods: We retrospectively assessed 161 pregnancies of diabetic mothers and 161 uncomplicated pregnancies matched by gestational age (control group). Diabetic mothers were allocated to three different groups: 1. diet-controlled gestational diabetes, 2. Insulin-dependent gestational diabetes, and 3. pre-existing diabetes. The anteroposterior thymic and the intrathoracic mediastinal diameter were measured and we calculated the quotient as thymic-thoracic ratio (TT-ratio). Furthermore, we defined the thymus-head ration (TH-ratio) as the quotient of the anteroposterior thymic diameter and the circumference of the fetal head. Results: TT-and TH-ratios were significantly smaller in pregnancies with maternal diabetes (P < 0.001 and P < 0.001, respectively). In all three diabetes groups, both ratios were lower when compared to the control group (P < 0.001). Conclusions: TT-and TH-ratios were significantly smaller in pregnancies with maternal diabetes (P < 0.001 and P < 0.001, respectively). In all three diabetes groups, both ratios were lower when compared to the control group (P < 0.001).