The only thing I have heard is that male sperm tend to be faster swimmers, but more fragile whereas female sperm are slower swimmers, but much hardier. So, if you want to increase the chances of having a girl, then DTD a couple of days before O (female sperm will be more likely to be around when the egg comes down). If you want to increase the chances of having a boy, then DTD on your O date.
We DTD 2 days before O, so we'll see what happens. We didn't do that on purpose to try for a girl, it's just the way it worked out. I know we DTD on our O date with ds2. I was not charting at all with DS1, so I have no idea how the timing worked on that one.
Melissa , wife to Tom , mom to The Baron , the Bean , Little Bear , and Baby Beaver