Because couples trying to conceive often have sex on demand when they're trying to maximize intercourse during a woman's fertile period, sexual lubricants can sometimes be helpful. But it's important to realize that the very thing that might be facilitating sex could be hampering the baby-making process.
That's because, according to the World Health Organization, the optimal pH for vaginal mucus to be hospitable to sperm is between 7.0 and 8.5 [source: Ellington]. However, many store-bought lubricants have a pH below 7, which can throw the vaginal chemistry out of whack and lead to impaired sperm motility and even sperm death.
One lubricant that is safe for baby-making sex is called Pre-Seed, and it has the same pH and consistency of vaginal secretions.