According to BabyCenter, creamy cervical mucus negatively affects the ease of movement for sperm toward an egg for implantation, and decreases the chances for fertilization. Creamy cervical mucus can range from pearl white to creamy yellow and is thick in consistency like lotion. Cervical mucus with the consistency of egg whites is the most desirable when the intent is fertilization.
Estrogen stimulates the secretion of fluid from the cervix. BabyCenter explains that the consistency and quality of cervical secretions can be used to evaluate fertility throughout a woman's menstrual cycle. Cervical mucus can be clear and watery, stringy (like egg whites), creamy, or thick and sticky. While egg white cervical mucus is the best for fertility, sperm are able to swim through clear and watery cervical mucus without much resistance. Either of these types of cervical mucus protects the sperm from hostile pH levels on its journey to the egg. Creamy and gunky cervical mucus make the sperm's journey much more difficult and significantly decrease the chances of fertilization. These types of cervical mucus are signs that the woman's peak window of fertility has closed until the next cycle.
The American Pregnancy Association points out that women hoping to become pregnant can check their own cervical mucus to determine its quality and assess whether it is likely to increase the odds of fertilization.