9. Morning Sickness Is The Best Pregnancy Test
Any rom-com movie that features the protagonist getting pregnant will almost inevitably feature a scene where said woman suffers a sudden bout of morning sickness, causing her to realise that - surprise! - she's pregnant.
Outside of actual viral thrillers like Contagion, there's basically no other reason you'll see a woman vomit on screen.
It's almost exclusively because she's pregnant, and it'll happen like the day after she's had sex with someone, where she'll initially assume it's a stomach bug.
This is quite blatantly exemplified in Knocked Up, where mere minutes of screen time after Katherine Heigl has sex with Seth Rogen, she's shown violently vomiting...twice, prompting her to take a pregnancy test and confirm the truth.
Generally speaking, morning sickness doesn't show up until around 8 weeks after conception has been achieved, and studies suggest that "only" 60-70% of women actually end up vomiting at all during their pregnancy.
Perhaps the only movie in history to do anything interesting with this trope is Fargo, where pregnant cop Marge (Frances McDormand) almost blows chunks while inspecting a gnarly crime scene, only to tell her partner it's just the pregnancy nausea.