Changes in twinning rate: Italy 1950-1996

Area of Science:

• Demography and Population Studies
• Reproductive Epidemiology
• Human Fertility Research

Background:

• Twinning rate has been debated as a potential monitor of population fertility.
• Developed countries observed a decline in spontaneous twinning rates from the 1950s to the late 1970s, potentially linked to decreased maternal age and family size.
• Twinning rates began rising in the 1980s, largely attributed to assisted reproduction technologies, especially among older mothers.

Purpose of the Study:

• To analyze the temporal trends in twinning rates within the Italian population.
• To investigate the relationship between twinning rates, maternal age at delivery, and birth order in Italy.

Main Methods:

• Analysis of temporal trends in twinning rates.
• Statistical examination of the correlation between twinning frequency, maternal age, and birth order in Italy.

Main Results:

• The recent increase in twinning rates is primarily associated with the use of assisted reproduction techniques.
• This association is particularly evident in the twinning frequency observed among older primiparae (first-time mothers).
• The twinning rate among young mothers has returned to levels observed in the 1950s, considered indicative of natural fertility.

Conclusions:

• Assuming twinning rate reflects fertility and population fitness, the data suggest a slight increase in natural fertility in Italy.
• Assisted reproduction significantly influences current twinning rates, especially in older maternal age groups.
• The convergence of twinning rates in young mothers to historical levels may indicate a subtle rise in underlying natural fertility.