As we learn at the novel’s climax, the man who impregnated Geneviève
Naud was not the dead youth, Albert Retailleau, but an older man,
Alban, who is married (though long separated from his wife) but far
better off financially than Albert and much closer to the Nauds in
social status. Alban and Geneviève have hatched a plot so that she
seduces Albert and gets him to believe that he’s the father of her
unborn child. But what’s the point? Wouldn’t it be much more sensible
if the parents simply leaned on Alban to get a divorce and marry
Geneviève? (This is apparently what happens at the end of the book
anyway.)
And if she’s only three months’ pregnant, that seems to
give her a ridiculously short time to (a) discover her pregnancy, (b)
hatch her plot with Alban, and (c) have an affair with Albert long
enough so that her claim that he made her pregnant is credible. When
Maigret learns from a buddy of Albert that his affair with Geneviève
began the previous October, roughly three months before the January in
which the novel takes place, both the biology and the chronology become
impossible----unless you want to believe that she knew she was pregnant
the moment the sperm met the egg.