In real life, if you crave sweets during pregnancy, you're supposedly due for a girl, but if you crave savoury things it will be a boy. Another belief: Carrying high leads to a girl, while carrying low is a boy. Surprisingly, superstitions like these can be found within games like The Sims, too. Source
Sims players have held weird beliefs about sim pregnancies for years now, and much of it seems to stem from the need for control. In my experience with The Sims, I always wanted to manage the gender of my sim kids. Girls not only had better clothes in the base game, most of the mods I cared about were for better makeup, and better hair.
The need to control pregnancies and to develop specific narratives is a common one among Sims players, especially given the popularity of the Legacy challenge. In the Legacy Challenge, you are tasked with playing the same family for 10 generations on a single lot, and you have to elect an heir from each generation to carry the family on. Especially in The Sims 3, where traits from sims can be passed on through birth, having two or more babies at once could up your chances for a worthwhile heir. Having twins became a hot commodity, but players needed a way to ensure pregnancies would give them the right result.
And so rumours about how to control pregnancies have propagated among fans. Back in 2004's Sims 2, many players believed that if you ate cheesecake or potato chips during pregnancy you'd end up with twins. Other players believed that in order to get twins, you needed to WooHoo in a fancy bed, or even a hot tub to get them. As far as I can tell, some players still believe all these things.
While the jury's out on potato chips, fancy beds and hot tubs, the cheesecake thing is, against all odds, 100 per cent true. The Open For Business expansion added cheesecake, with the official game guide noting that it would increase the chances of twins. What actually ended up in the game was that eating cheesecake would guarantee twins if eaten after conception. Modder TwoJeffs made a patch that fixed the bug, confirming the cheesecake thing's existence in the process.
As far as determining gender, this article from Mod the Sims, a popular resource for Sims mods, notes that you can either use cheats or essentially save scum your babies until you get the one you want.
Lucky for me, in The Sims 3, players were finally given options to influence a baby's gender. The existence of an actual mechanic somehow only created more whispers about what may or may not be possible within The Sims. This time, the rumour was that if you ate apples during the first trimester, you'd end up with a boy, while if you ate watermelon it'd be a girl.
To wit, I force fed my pregnant sims raw watermelon back in 2009 and always ended up with girls. I don't know if that's because it actually worked or just a coincidence, but my sims never seemed happy about eating 10 slices of raw watermelon right after WooHooing.
At last I could ensure that I got to play around with all the new makeup and hair I'd added! I don't remember specifically where I heard this rumour, but I'm guessing it was from Carl's Sims 3 Guide, a fansite that attempted to comprehensively organise all the possible tips, tricks and rumours from the game.
If you wanted twins, Carl's Sims 3 Guide noted to make sure the mum was surrounded by kids stuff. Have her watch the kids' channel on TV, read books about pregnancy and listen to the kids' radio station and she'd be sure to pop out two or more kids. The Sims 3 also had the option of buying your sims "Lifetime Rewards", special traits you could add to your sims in exchange for completing a certain amount of their wishes. One of these was a "Fertility Treatment", which was a less tedious method of increasing the chances of twins or triplets.
While most players swear by the apple and watermelon method, its hard to confirm that it really works. Players are convinced that it works, though, and have documented attempts to prove it. Modder J.M. Pescado seemed convinced based on his own research, writing, "There's a cheesecake effect at work. Eating foods containing 'watermelon' increases the chance of females, eating foods containing 'apple' increases males." While the devs would acknowledge cooked foods increasing the odds of one gender or another in a patch note, I hadn't ever read that the raw versions of these food would work. I also haven't seen confirmation on any of the methods for getting twins, and even buying Fertility Treatment seems dicey.
When I asked on Twitter, one player independently confirmed that the apple and watermelon method did work for them.
This was corroborated, finally, by The Sims's dev team when I reached out and asked them. "We're The Sims and love adding goofy things in the game, and thought it would be fun to add a way to modify pregnancy in terms of gender and twin probability," they said. "Otherwise, gender is determined 100% randomly at birth and probability may not always work in your favour."
While the method to influence gender in The Sims 4 was announced in a patch note on May 4, other methods, especially the one from The Sims 3, are still shrouded in mystery. In real life, we've got innumerable old wives tales about pregnancy. Who's to say that our sims don't have them too?