Since the 1980s, there has been an increase in twin pregnancies. While before there were about 20 cases for every 1000 newborns, in the years '10 of 2000 it went to 35 per 1000. The trend has raised some concerns, given that these gestations have on average more complications. We also ask ourselves what the causes are. Only for the increase in the number of couples using IVF?
Dr Eli Adashi and Roee Gutman of Brown University's Warren Alpert Medical School analyzed data on twin pregnancies. The aim was to determine how in vitro fertilization affected the increase in cases. It emerged that IVF is only part of the fault. The increase would actually be due to the rise of the average age of future mothers, it would therefore be largely natural and the result of a social phenomenon.
It has been known for a long time that more adult women are more likely to incur twin pregnancies. There are even 150-year-old articles on the subject. Nevertheless, the phenomenon has been analyzed little and without measurable statistical data. Until today, at least. The study of the two doctors in fact starts from the data collected in periods in which the IVF did not exist.
The starting point was the pregnancies between 1949 and 1966, before assisted fertilization. The researchers found that women over the age of 35 had 3 times the chances of having twin births. The odds were 4 times greater in the case of African American women. Usually the children were twins who were heterozygous and therefore not identical.
Later, researchers analyzed data from 1971 to 2016. In times of great social change, there was a higher rate of 30-40 year old mothers. The percentage rose from 14% in 1971 to 42% in 2015 (31% among African-American women). This phenomenon is also accompanied by an increase in in vitro fertilization and the number of twin births.
In vitro fertilization contributed to the increase in twin births. Yet in 2016 it seems to have been the cause of only 24% of these.