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Meiosis vs. Mitosis

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Cell division is necessary for growth and reproduction in organisms. Mitosis aids cell growth and development by dividing somatic cells. In contrast, meiosis causes the division of germ cells and plays an essential role in sexual reproduction. Due to their unique functional requirements, mitosis and meiosis differ from each other in multiple aspects.
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During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed sister chromatid separation during meiosis II. In some species, notably plants, nondisjunction can result in an organism with an entire additional set of chromosomes, which is called polyploidy. In humans, nondisjunction can occur during male or female gametogenesis and the resulting gametes possess one too many or one too few chromosomes.

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Sequential testing for Down syndrome: the impact on estimated risk.

Stephen T Chasen¹, Shane Wasden

¹Weill Medical College of Cornell University, Department of Obstetrics and Gynecology, New York, NY, USA. stchasen@med.cornell.edu

Prenatal Diagnosis

|March 16, 2012

Summary

This summary is machine-generated.

Sequential testing effectively reduces estimated Down syndrome risk, particularly when initial first-trimester screening shows lower risk. This approach refines risk assessment for expectant parents.

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Area of Science:

Prenatal diagnostics
Maternal-fetal medicine
Genetics

Background:

First-trimester screening is a common method for assessing Down syndrome risk.
Sequential screening offers a follow-up assessment to refine risk estimations.
Understanding the utilization and impact of sequential testing is crucial for improving prenatal care.

Purpose of the Study:

To describe the utilization patterns of sequential screening in prenatal diagnostics.
To evaluate how sequential screening impacts the estimated risk for Down syndrome.
To analyze the relationship between initial risk and the effectiveness of sequential testing.

Main Methods:

Retrospective review of records for patients undergoing first-trimester screening over a 3-year period.
Comparison of adjusted first-trimester Down syndrome risk with adjusted risk after sequential testing.
Statistical analysis using Fisher's exact test and chi-square for trend.

Main Results:

Sequential testing was utilized in 34.0% of 12,557 patients.
Sequential testing increased Down syndrome risk in 13.1% of cases, with a doubling of risk in 5.2%.
The likelihood of increased risk with sequential testing decreased as initial first-trimester risk declined (p < .001).

Conclusions:

Sequential screening generally lowers estimated Down syndrome risk.
The effectiveness of risk reduction through sequential testing is more pronounced with lower initial first-trimester risk.
Sequential testing provides a valuable tool for refining Down syndrome risk assessment in pregnancy.