How to Have a Baby Girl in Sims 3by Seth Amery ; Updated September 22, 2017
Making a baby in "The Sims 3" is the easy part; trying to influence its gender during the pregnancy is a completely separate beast, especially while trying to keep mom-to-be happy. Although there is no way to guarantee you'll get a baby girl instead of a boy, there are a few actions your Sim can take in an attempt to tip the odds.
Attempting to Have a Baby
Although your Sim's future sleeping schedule would argue against the idea, you don't have to be married or even be in a romantic relationship to make a baby with another Sim. Any Sim who is at least a Romantic Interest can be a parent to your Sim's child. Keep using romantic interactions until the other Sim finds yours "extremely irresistible"; this opens up the "Try for Baby" interaction. If successful, you'll hear the unmistakable tune play after the PG-rated animation completes.
Influencing Gender Towards Female
By default, unborn Sims have a 50/50 chance of developing into a boy or girl. If you're hoping for a girl, have the mother start on a watermelon regimen; eating at least three during the three-day pregnancy places heavier influence toward girls, though there will still always be a chance for a boy. A Sim who is at least Level 5 in the Medical career can determine the gender of the unborn baby. If you're told it's a boy, try eating watermelon anyway; this can increase the odds of having twins of each gender. Avoid apples at all cost, which increase the odds of having a boy.
Caring for the Mother During Maternity
Between all the watermelon meals, mom doesn't have to worry about keeping well-fed. She'll get the next few days off work, so you don't need to worry about having a second set of hands around, either. The first day, she'll experience nausea and should be kept near a restroom; to combat the negative moodlet, try having her read fiction or watch television near the most convenient restroom. The next days will involve back pain, easily relieved with a spa day or a massage from a significant other. By the end of day three, be prepared to welcome your new baby to the world.
Keeping the Baby Quiet Until She's Eighteen
Just kidding -- she's going to develop a Want to learn how to drive as soon as she becomes a Teen Sim. In the meantime, making sure the baby is fed and played with twice a day takes care of most of her needs. To replenish the baby's hygiene, you'll need to change her diaper. Unlike human beings, Sim babies have the benefit of displaying visible Need bars that tell you exactly what they're crying about -- fewer guessing games and more relaxation for mom while Baby sleeps.