Are 'natural' twinning rates continuing to decline?

Area of Science:

• Reproductive Epidemiology
• Demography
• Public Health

Background:

• Maternal twinning rates declined globally in the mid-20th century.
• A reversal occurred around 1980, with increasing twinning rates observed subsequently.
• The rise in twinning rates raises questions about the role of assisted reproductive technologies versus natural trends.

Purpose of the Study:

• To investigate whether the recent increase in twinning rates is attributable to assisted reproduction or a rise in natural twinning.
• To explore the potential of natural twinning rates as an indicator of reproductive health.

Main Methods:

• Utilized indirect methods to estimate natural twinning rates due to lack of nationwide data on medically assisted conceptions.
• Assessed trends in England and Wales, and Belgium.
• Employed specific assumptions regarding medical assistance prevalence in young women (England and Wales) and regional variations (Belgium).

Main Results:

• Tentatively concluded that natural twinning rates have recently increased in England and Wales.
• Tentatively concluded that natural twinning rates have recently increased in Belgium.
• Highlighted the need for direct data to validate these findings.

Conclusions:

• The increase in twinning rates may reflect a rise in natural twinning, potentially signaling changes in reproductive health.
• Further research with direct data on medically assisted conceptions is required to confirm the observed trends in natural twinning.