Can female orgasm prevent conception or implantation?

No. There is some indirect evidence it may help conception. The horizontal position may aid sperm in reaching the cervix. There is also evidence that the vaginal/pelvic contractions help retain semen in the vagina.

Related Questions

Does a female orgasm liquid act like fertile cm? Does it help conception happen sooner?

No, sort-of... For years we've known orgasmic vaginal fluid to be less acidic than regular vaginal pH (3.8-4.5) which theoretically would increase survivability of sperm. Semen itself is the best sperm protector with a pH of 7.2-7.4 (neutral, relatively basic in comparison). This is unlikely to make much of a difference given the sheer volume of ejaculate deposited at the cervix's front door. Timing = everything. Read more...