In a 2018 study published in the American Journal of Obstetrics and Gynecology (Am J Obstet Gynecol 2018 Nov, 219 (5): 469 (e1-10) by Numi et al from Finland evaluated the recurrence risk of hyperemesis gravidarum (HG) in subsequent pregnancies. The recurrence risk is wide, ranging from 15-81%, depending on study settings. Of the 4103 pregnancies investigated in 1836 Finnish women, the findings reported were 24% of women suffered a repeat.
Some women, while considering additional children, simply chose not to face the possible risk of another unpleasant experience.