There were many episodes throughout the show that dealt with not only premarital sex, but more importantly, the consequences surrounding it; namely, pregnancy and HIV/AIDS. The show also dealt with the topics of sexual harassment and sexual assault.
PREGNANCY:
Melissa Coolidge (S1E12)
This episode was the first to deal with unplanned pregnancy when Brandon meets a new girl, Melissa. She's beautiful, smart, Harvard-bound-and a young mother. On the day of her Harvard interview, Brandon is forced to watch her son, Joey, when her babysitter gets sick. Melissa is shown to struggle with being a teen mom, even considering giving her child up for adoption. But, eventually she decides not to, as he is a part of her.
Brenda Walsh (S2E1):
Brenda feared she was pregnant at the beginning of season 2. After taking a home pregnancy test that came up inconclusive, Kelly took her to a gynecologist, who confirmed that Brenda was not pregnant, much to everyone's relief. However, the scare was enough to make Brenda feel that she and Dylan are moving too fast and she breaks up with him.
Jackie Taylor Silver (S2):
Kelly's mother Jackie discovered she was pregnant in the winter of Kelly's junior year of high school. After initially hesitating to tell the father, Mel Silver, they become engaged and marry in the season finale. The first of the season 3 summer episodes shows Jackie going into labor at the end of the episode, and the next episode revealed she had a baby girl, Erin.
Andrea Zuckerman Vasquez (S4):
Andrea first finds out she's pregnant in "Thicker Than Water". After briefly considering an abortion, she and her boyfriend Jesse decide to marry. Andrea goes into preterm labor in "Acting Out" and is immediately put on bed rest. In "Vital Signs", she is put into the hospital, but her water breaks at the end of the episode. Hannah Rose Zuckerman-Vasquez was born at the beginning of "Mr. Walsh Goes to Washington" 3 months early.
Kelly Taylor (S7E29):
Kelly is terrified in the episode "Mother's Day" when a pregnancy test comes back positive. She decides to get an abortion, even though boyfriend Brandon promises to be supportive. But before the pregnancy can even be confirmed, Kelly learns at her doctor's appointment that she has miscarried.
Leanne (S8):
Leanne was a pregnant teen that came into the free clinic where Kelly worked. Leanne fled when Kelly went to go get the doctor. Hours later, Kelly discovers Leanne's baby, a little boy, on the doorstep of the clinic. She turns him over to foster care and applies to be the baby's foster mother. The baby is instead given to a gay couple. Leanne, who had previously shown no interest in taking responsibility for the baby, then decides she wants her baby back. Kelly comes to learn this is only because she does not want the baby raised by gay parents. Leanne then decides, after talking to Kelly, to give the baby back to the couple.
Janet Sosna Sanders (S10):
Steve's girlfriend janet found out she was pregnant in the season 10 premiere. After an initial hesitance, she allowed Steve to be involved and accepted his marriage proposal. They married in episode 8, and she gave birth the next episode to a daughter named Madeline while on their honeymoon.
HIV/AIDS:
Season 1, Episode 10 "Isn't It Romantic?" January 3, 1991
This one was the first, but certainly not the last, to bring up the topics of sex and AIDS. While the main plot of the episode involved Brenda and Dylan becoming a couple, the subplot involved Stacy Sloan, a guest speaker at West Beverly. When Steve is assigned to pick her up, he flirts with her, but she politely turns him down. She later reveals to the audience that she has AIDS.
Jimmy Gold (S7):
In season 7, Kelly volunteered at an AIDS hospice and befriended AIDS patient Jimmy Gold (Michael Stoyanov). She takes an HIV test herself after accidentally getting blood on her hand helping Jimmy with a cut. She felt bad for shunning Jimmy, and in episode 5, he dies, presumably with Kelly by his side.
Valerie Malone (S8):
In the season 8 finale, Valerie learned that a former partner, Johnny, was HIV-positive. With David's support, she is tested for HIV. It ends up coming back negative.
Sexual Harassment:
Kelly and Dr. Monahan (S8):
Monahan was a doctor at the free clinic where Kelly worked. One night, he makes a pass at her while examining her shoulder. Kelly files sexual harassment charges against him. He leaves and is replaced with Donna's father.
Sexual Assault:
S1E13 "Slumber Party"
During a slumber party at Brenda's, Kelly reveals her first time. The senior football star, a guy she really liked, took her out in the woods and date-raped her, never speaking to her again afterwards. This is brought up again in the season 8 episode "Reunion" when Valerie discovers old graffiti, revealing the rumors spread about Kelly. Valerie puts the guy, who attends the reunion, in his place.
S2E13 "Halloween"
Kelly faced unwanted sexual advances at a Halloween party. Once alone with the young man, he pushes her down on the bed, but Brenda and Donna walk in before he can do anything. Steve punches him.
S8:
One night at the After Dark, Valerie apparently sleeps with Noah in her office, although she doesn't remember it. When she experiences flu-like symptoms, David takes her to the doctor, who reveals she had the drug Rohypnol (commonly known as the date-rape drug) in her system. She immediately accuses Noah of rape and takes the case to court. After Valerie wins the case, Donna finds a prescription of Rohypnol on Noah's half-brother Josh, which clears Noah of all charges because Josh was the one who drugged Valerie. Noah, however, did cheat on Donna with Valerie
S9-S10:
Kelly was faced with the issue one more time when she was raped in a dark alleyway. She initially told no one, but slowly began to open up: first to Dylan, then to Donna and finally boyfriend Matt. Unbeknownst to both her and Matt, Matt is defending her rapist on petty crime charges. Not knowing the history, Matt sends the rapist, Joe Patch, to Now Wear This. As they recognize each other, Joe locks the door and pulls a knife. Kelly then grabs the gun Dylan gave her and fires at him until she is out of bullets, ending the season. In the season premiere, Kelly is arrested for murder, but the police declare it a justifiable homicide and let her go.