Insurance ovulation, embryo mortality and twinning

Area of Science:

• Reproductive Biology
• Human Genetics
• Evolutionary Medicine

Background:

• The 'insurance ova' hypothesis suggests dizygotic twinning results from selection for polyovulation to reduce fertilization failure or embryo loss.
• This hypothesis implies a potential covariation between embryo defect rates and twinning rates.

Purpose of the Study:

• To test the prediction that embryo defect rates and dizygotic twinning rates covary.
• To expand the 'insurance ova' hypothesis to include a model for the rejection of anomalous embryos.

Main Methods:

• Analysis of national-level data correlating twinning rates with rates of trisomy-21 (Down's syndrome).
• Statistical control for maternal age in the correlation analysis.

Main Results:

• A strong positive correlation was found between twinning rates and Down's syndrome rates, even after controlling for maternal age.
• This suggests that variations in twinning and Down's syndrome rates may be linked to early embryonic rejection mechanisms.

Conclusions:

• The findings support the 'insurance ova' hypothesis and suggest an expanded model incorporating embryo rejection.
• Individual variation in polyovulation frequency and embryo rejection efficiency may influence reproductive success and rates of twinning and chromosomal abnormalities.