In all published literature available to me it is stated that in 1848, Henry Hancock, President of the Medical Society of London, presented a paper to that society describing the treatment of a 30-year-old female eight months pregnant in the Charing Cross Hospital in London [Hancock H. Disease of the appendix caeci cured by operation. Lancet. 1848;2:380–2.].
In only one book (published in 1899) it is written that François Mestivier, in 1759, incised an abscess in the right groin, in a woman eight months pregnant, and on autopsy found at the bottom of the abscess, the appendix vermiformis perforated by a pin [Mestivier FF. Observation sur une tumeur, située proche à la région ombilicale, du côté droit, occasionée par une grosse épingle trouvée dans l'appendice vermiculaire du cécum. J Méd Chir Pharmacol. 1759;10:441-2.].
I cannot reach the full-text of that article to confirm that this is the first published case. In all texts that mention Mestivier's article, a male patient is described and there is no mention of pregnancy (of course).
Please if someone has the full-text of that article send it to me or if anyone has the knowledge of some earlier descriptions of appendectomy during pregnancy or postpartum inform me.