heres some info i found for you
also you can go to any dr and ask about it

they will all tel you that precum does contain sperm in it and no studies have proven otherwise (planned parenthood will also support this info)
Pre-cum or pre-ejaculatory fluid is released when a guy gets an erection. It cleans out the inside of the urethra, which is the tube that carries semen and urine out of the penis.
While having intercourse or just playing around, there are two kinds of fluids released by the penis. The first of this is the pre-ejaculate or pre-cum, which is a lubricant made by a gland in the penis. The second fluid is released during ejaculation and is semen. This fluid is made in the testicles and carries sperms along with any sexually transmittable infections
The pre-cum has enough of the swimmers to arrive at your uterus and the fallopian tubes. What’s worse is that the sperm can live for 3-5 days in a very favorable environment, like inside your wet womb. So even if you’re infertile, once the sperm touches the mucous in your vulva, which aids it in going inside your reproductive system, the sperm can thrive there. This makes conception eventually possible even if you had sex or were playing around several days before ovulation.
the way sperm gets into precum is when the precum ppicks up sperm inside the urethra of the mae and travels out into the vagina,thus a possiblity of pregnancy occurs