Large Families

Wikipedia lists 15 women who had more than 30 children. That includes a woman said to have had 69. Questionable as some of those may be there appear to be well substantiated cases of more than 20. As children of large families tend to have large families of their own the phenomenon is significant for genealogy.

In November 2016 the UK Office for National Statistics issued a Statistical Bulletin Childbearing for Women Born in Different Years, England and Wales: 2015. It concludes that women born in 1970 who completed their childbearing by 2015 had an average 1.91 children, fewer than their mother's generation (born 1943) who had 2.24 children. A graph shows the average number of live born children reaching a peak of 3.9 in 1935, up from 2.0 in 1920 where the data starts.
The bulletin also shows that 15% of women in the 1943 cohort had four or more children; for the 1970 cohort that figure was down to 10%.

This table, from an article A Hundred and Fifty Years of Vital Statistics: Documenting Demographic Change in Ireland, by John FitzGerald shows the decline in average completed Irish family size from 6.5 in 1911 to 2.5 in 2011.
The trend to smaller Irish families is reflected in the 2011 census data showing women in their early 50s most likely had 2 children, those from their late 50s to early 70s 3 children, and 4 for older women. The percent of women with 8 children in their early 50s was only a tenth of those in their 80s.

The 1911 census for Ireland has been digitized for fertility data, available at http://www.census.nationalarchives.ie/search/. The graph shows the number of children live-born to married women age 45 and older. Leaving aside child-free couples eight was the most likely family size. The largest family had 22 children; there were eight of 20 or more children.

As for Canada, with all caution regarding the credibility of the Huffington Post, here's their take on the Biggest Family In Canada.

What's the largest number of live-born children one woman had in your family tree. I asked that at a BIFHSGO get together on Saturday. From about 15 people the largest was 18.