Plot hole: When Ellie leaves Ft. Smith on a whiskey boat, she's just been seen with the morning sickness a day or two before. When she leaves the whiskey boat, somewhere between Arkansas and Nebraska, she says she's pregnant but is not showing at all. Even the snaggle-toothed frontier weirdo played by Steve Buscemi remarks that, "You ain't gonna be havin' no baby fer a while yet." The day she gets to Clara's, near Ogallala, Nebraska, she has the baby. Pregnancy lasts nine months. Morning sickness usually begins at about six weeks into it. Ft. Smith, Arkansas, to Ogallala is 561 miles. Even just walking three miles an hour for eight hours a day, one could make it in less than a month. But going via boat and mule-drawn wagon took her over seven months?
Revealing mistake: When they arrived at Montana, the Captain said that this is where we will stop and build a ranch. There are two straight depressions in the ground converging together that would not have been there since this was virgin land.
Answer: They didn't have antibiotics to prevent infections from setting in. No sterilized equipment. No clean rooms to work in. Everything was dirty.