This question was originally asked on Quora. Following is my first-hand experience.
There is a lot of chance involved in which gender your child will be, and much can be said for loving the child no matter what … NO MATTER WHAT! That being said, I really wanted boys. Knowing my own personality quite well by the time I approached conceiving at the ripe old age of 35, I knew I wanted boys. This was pre-Internet, and I wanted the latest research. I didn’t head for the library. I went to Barnes & Noble and sat in the parenting and childbirth aisle for a whole day. I scoured everything. Here’s what I learned:
The sperm that produce boys swim faster than the sperm that produce girls, however, they don’t live as long.
Timing the introduction of the sperm to the egg was critical for the desired outcome.
Female orgasm produces an environment in which sperm can travel faster and live longer. So, if the female has an orgasm before the release of the sperm, this favors the birth of boys.
Knowing the exact time of ovulation was necessary for this plan to work. I learned that I could tell when I was ovulating by watching for a mucous plug to be released from the cervix. This mucous plug was sort of the consistency of apple jelly and might have a tan-ish color. It wasn’t very big - less than a teaspoon in volume, but it was quite sticky.
Now here’s the part that’s tricky to explain. Let’s call the day the plug is found Day 1 - this is the day the egg is released from the ovary. If I have sex on this very day, it’s pretty much 50/50 on the gender of my baby. The egg is traveling south, and all the sperm traveling north … the odds are good that both male and female producing sperm will still be active.
If I have sex on Day 2, the egg will have traveled south a good bit and will encounter the fast swimming and more active male sperm first. My odds for producing a boy child were much better.
Since you want to have a girl, this may need a few months of watching the signs for ovulation. Introducing sperm at the earliest possible moment (like the day before ovulation) would allow the female swimmers to reach the egg soon after its release. The male sperm would be less likely to swim that far and last that long. It is possible that if the female resists having an orgasm, this could also tilt the odds towards having a girl.
By the way, I have two healthy boys.