Factors Affecting First Trimester Maternal Serum Down Syndrome Screening Results - Obstetrics and Gynecology

More Info

---

The first trimester maternal serum screening for Down syndrome, also known as the first-trimester combined screening, is a crucial test that assesses the risk of chromosomal abnormalities, particularly trisomy 21 (Down syndrome), trisomy 18, and trisomy 13. The results of this screening are influenced by several factors, and understanding these can help alleviate concerns about the accuracy of the results.


Factors Affecting Screening Results
1. Maternal Age: One of the most significant factors is the age of the mother at the time of delivery. The risk of chromosomal abnormalities increases with maternal age, particularly after age 35.

2. Gestational Age: The timing of the test is also critical. The first trimester screening is typically performed between 11 and 14 weeks of gestation. Accurate dating of the pregnancy is essential for interpreting the results correctly.

3. Biochemical Markers: The screening involves measuring specific substances in the mother’s blood:
- PAPP-A (Pregnancy-Associated Plasma Protein A): Lower levels of PAPP-A may indicate an increased risk for Down syndrome.

- Free β-hCG (Beta-human chorionic gonadotropin): Elevated levels can also suggest a higher risk for Down syndrome.

- The combination of these markers, along with ultrasound measurements, is used to calculate the risk.

4. Ultrasound Findings: The nuchal translucency (NT) measurement, which assesses the fluid at the back of the fetus's neck, is another critical component. An increased NT measurement can indicate a higher risk for Down syndrome and other chromosomal abnormalities.

5. Maternal Weight and Ethnicity: Maternal body mass index (BMI) and ethnic background can also influence the levels of the biochemical markers and the overall risk assessment.

6. Previous Pregnancy History: A history of previous pregnancies, particularly those with chromosomal abnormalities, can also affect risk calculations. However, the number of previous pregnancies is typically not a direct factor in the calculation but may be considered in the context of overall risk.


Impact of Incorrect Information
In your case, the incorrect entry regarding the number of previous pregnancies (indicating 2 instead of 1) may not significantly impact the screening results. The primary factors that influence the risk calculation are maternal age, gestational age, and the biochemical markers. However, it is always best to correct any inaccuracies in medical records to ensure that healthcare providers have the most accurate information when interpreting results.


Recommendations
Given your concerns about the accuracy of the screening results, it is advisable to discuss this with your healthcare provider. They can provide guidance on whether a repeat screening or additional testing, such as non-invasive prenatal testing (NIPT) or chorionic villus sampling (CVS), is warranted based on your specific situation and risk factors.

In summary, while the number of previous pregnancies is a factor in the overall context of maternal health, it is not a primary determinant in the first trimester Down syndrome screening results. Focus on the more critical factors such as age, biochemical markers, and ultrasound findings for a more accurate assessment. Always consult with your healthcare provider for personalized advice and to address any concerns you may have regarding your pregnancy and screening results.