It is unlikely that Elizabeth wouldn't know she was pregnant. However, I
wrote this ending in response to Austen tributes that I feel completely
misinterpret Austen and her time period (likewise, the final chapter of
Persuadable is a response to the 2007 movie).
Because Austen deliberately left out hot & heavy romance scenes as
well as direct discussions of topics like reproduction (there are plenty
of indirect discussions), many readers assume (1) that Austen belonged
to the Victorian era; (2) that Austen, the spinster, was
repressed/scared of sex, etc.
Setting aside that Victorians were far more earthy and cognizant of
basic human functions than many modern people seem to be and also
setting aside that Austen was not actually a Victorian but belonged to
the earthy, sometimes bawdy, Regency era and setting
aside that Austen was surrounded by all kinds of sex-related scandals
and could have written the equivalent of salacious porn if she'd wanted
(and writers of that era did), Austen deserves to be treated as what she was: a serious writer.
She didn't write what she did because she was a poor little woman with no experience; she wrote what she did from choice. Everything that is excised from Austen is excised by the author's careful craftsmanship.
So when I read Austen tributes that paint Darcy as some kind of stuck-up
Victorian prig whose introversion has been translated into sexual
repression, I want to scream.
Part of the problem, I believe is that many American (and some British)
authors translate Darcy's wealth into American terms; they think the
Darcys are the equivalent of the Vanderbilts and Rockefellers, families
whose wealth originated in industrialization and who used that wealth to
create ostentatious and decadent lifestyles in places
like Newport, Rhode Island.
But Darcy grew up on a farm! His wealth is based on land, crops, weather, and other such earthy considerations. He would be fully cognizant of the ways of reproduction; he would likely have seen newborn babies; he would more than likely have seen tenants' wives breastfeeding (remember, Darcy rode his horse all over Pemberley when he was a youth).
Colin Firth's Darcy likewise--and correctly--has a very easy manner with his servants. All parties take for granted that Darcy is in charge. He also interacts with them as people whom he works next to every day, not invisible entities that need to stand in corners while the upperclass indulge in frivolities (a far later custom, belonging to the late Victorian and Edwardian eras). They like him because he is a good manager.
We moderns like to believe that we are so much more aware of things than
people of the past, but the truth is, Austen doesn't talk about a lot
of stuff in her writing precisely because she wouldn't have considered
it quite so shocking and astonishing and hush-hush as us.
Excerpt from "Darcy Betrays a Thorough Understanding of Human Biology"--
“Maybe you’re starting a baby,” Darcy said and headed towards the door.
He was halfway across the room when Lizzy said, “Will!” and he turned back. She sat on the divan, staring at him, her face pale, eyes large.
“I think you’re right,” she said, slightly stunned.
Darcy shook his head. Why was she surprised? Her mother was fertile—she had given birth to five healthy daughters and survived.
He went back and kissed the top of his wife’s head. He was pleased, though babies at this stage always seemed rather remote to Darcy. He usually visited them in his tenants’ cottages after their births, bestowing coins, best wishes, and the occasional sapling.
Of course, this baby—his and Elizabeth’s baby—would garner far more attention and resources than Darcy had ever marshaled before. But Darcy rather liked the idea of introducing a new relation to the delights of Pemberley.
“I’ve never had a baby,” Lizzy said to his shirt, which made Darcy laugh. She grimaced up at him. “I’ve taken care of children, but this—”
“Lizzy,” Darcy said, still amused, “you can do anything.”
She laughed then and pushed him away: “Get along, you.”
Darcy went out to find the castile soap. As clever as his wife was, he thought as he ran down the stairs, there were times when she could be downright obtuse.