I've never counted all my bridal pregnancies throughout time, but at a quick estimate I think it could be as a high as around 30% ( it's definitely over 20%) of all my family lines if I go back from the early 1900s to the 1700s that the bride was pregnant with the eldest child.
It was extremely common throughout all the generations
Even my grandmother was heavily pregnant when she walked up the aisle with my grandfather ( she was carrying my parent's oldest sibling - who is 100% my grandfather's child, my 1st cousin has taken a DNA test) .
I can quite imagine my great grandmother , old Mary doll ( who was short ) rounding up my grandfather ( 6ft, and a soldier) with a shot gun quite easily ( she grew up on a rural farm so did my grandmother , until Mary's husband died ) and marching him down the aisle to marry her daughter LOL . Poor granddad , he didn't stand a chance lol
Mary was apparently one real tough cookie and brought up my grandmother and siblings with a very strict hand ( my parent knew Mary and she was even a tough cookie in old age ) . She had to be, she brought up a young family by herself with mouths to feed , her husband , my gran's died father, died when my gran was just 4 years old and she never remarried, she brought all the kids up by herself in a time when there was no help.
My gran kept that one a secret, lol sly old dog lol ( I knew my grandparents very well , we were close). I only found out , years ago when I decided to get my grandparent's marriage cert that my gran had to be 7 months pregnant - the bump would have been definetely be showing ( and they married in the local church lol).
One of my grandmother's sisters had just turned 17 years old when she gave birth ( who has also tested but I am not going to ask my 2nd cousin about the dna on her parent's fathers side, to see if the father is actually the real father of her parent). The mother ( my grandmother's sister) got married a few days after the birth - the birth of this child actually has a note on their cert, saying the parents got married at so and so date ( a date after the birth) - so that it could be registered with the father's name. It's the first one I've ever seen one like this where the registra makes a note of them marrying days after , written on the actual child's birth cert. ( I have both the birth and the marriage cert) .
I think that was was definitely a shot gun wedding, whether he is the bio father I don't know, or if he stepped in to marry her , but I think he probably is the real bio father ,as this side of my family had a real habit of marrying off their young girls to the local old men farmers . ( the man she married was 51 years old).. She was just little more than a kid, just 16 yrs old when she fell pregnant to what would be considered to be a very old man to a 16 yr old child. Today it would be totally frowned on.
I can remember when I was a child, old ladies ( around my grandparents generation) would tut tut tutting at the younger generations who fell pregnant, saying "that would never happen in my days" Lol .
It happened throughout all generations, and was extremely common in their generation too , except its perfectly acceptable now, and not covered up like they used to do.
Kind regards