Factors predicting a positive pregnancy screening test at first trimester

Background: For every pregnant woman, it is possible to have a child with chromosomal abnormalities. Although this possibility is not very high, by performing screening tests and considering the mother's background factors, we can largely realize the real extent of this possibility. Many comorbidities (like high blood pressure, diabetes, and obesity) and high-risk exposures (like alcohol consumption) seem to have an important role in the development of chromosomal abnormalities. This study aimed to determine the predictive factors of a positive first-trimester screening test in the pregnant women. Methods: This case-control study was done on pregnant women, who were referred to Yas Hospital for their first-trimester screening tests between April 2018 and February 2020. Of those who had positive screening test results, only ones with abnormal biochemical tests, were included in the study regardless of nuchal translucency (NT) examination results and were considered as cases, and the women with normal screening test results were considered as controls. Results: Totally 960 pregnant women (760 controls and 200 cases) participated in the study. The mean age of the subjects was 31.07±0.17 years old with a minimum age of 17 and a maximum age of 45. The averge age of case group women was 33.57±0.40 years and this was 30.41±0.18 years in control group. This study indicated that maternal age (P<0.001) and the number of pregnancies in the case group are significantly (P<0.001) higher than the control group. Also, having a history of miscarriage (P<0.001), having a history of infertility (P<0.001), and having hypothyroidism (P=0.030) are significantly more common in the case group. The frequency of intrauterine growth failure (P=0.003) and neonatal hospitalization (P<0.001) were also significantly higher in the case group. Conclusion: Despite recent advances in the prenatal field, the accuracy of screening tests may still vary depending on maternal age and other existing characteristics. Hence, it seems considering the mother's background characteristics are important just the same as the screening test results.