Carol, Ross' ex-wife, visits Ross at the museum where he works to tell him that she is pregnant. Ross is shocked at the pregnancy, but Carol says that she and her lesbian life partner Susan want him to be involved, but only if he is comfortable with it.

Meanwhile, Monica frantically cleans the apartment as her and Ross's parents Jack and Judy are coming over for dinner and she is worried that they will be critical about the cleanliness of her home. Rachel looks around the apartment for her misplaced engagement ring so she can give it back to her ex-fiancé Barry the next day, and remembers she had it on earlier that morning when she was in the kitchen making lasagna. Realizing the ring is in the lasagna, Monica is upset with Rachel for ruining her parents' dinner while the others find the engagement ring in the lasagna. Ross arrives and tells everyone Carol is pregnant, and informs them that Carol and Susan have invited him to go to their first sonogram appointment the next day. He is still processing the fact that he has become a father, and does not know where he fits in with two lesbian mothers.

Later that night, Monica and Ross have dinner with Jack and Judy, the latter criticizing Monica throughout. After much pressure from Monica, Ross eventually reveals that Carol is a lesbian and that she is pregnant with his child and plans on raising it with Susan. Rather than responding to Ross, Judy accuses Monica of not telling them.

Meeting with Carol and Susan at the sonogram, a hesitant Ross asks how he can be involved. When he asks about naming the child, Carol and Susan give first names that Ross says will sound silly with his surname Geller. Carol and Susan break it to Ross that his surname will not be used as they intend to use their names Willick-Bunch, with Susan spitefully telling him that the baby is hers too. Ross realizes he is not ready to be involved and turns to leave as the doctor finds the baby's heartbeat. He stays and decides to become involved. At Monica and Rachel's apartment, Ross brings over a video of the sonogram and the group watch it on TV.

Meanwhile, Rachel visits Barry at his dental practice to return her ring and apologizes for running out of their wedding, feeling bad for him going on their honeymoon alone. Barry reveals that he went on their honeymoon with Mindy, Rachel's best friend and maid of honor, who he has been seeing. Rachel talks to Mindy on the phone and tells her that if everything works out and the two get married, she hopes their kids will have Barry's receding hair and Mindy's old nose. Rachel hangs up and despite knowing it is a cheap shot, feels better for saying it.

In the original broadcast, the episode was viewed by 20.2 million viewers and achieved the rating of 14.0. The reviews for the episode were mixed. The A.V. Club noted in its review that the episode "seems a far more run-of-the-mill sitcom episode—definitely formulaic, and in places sadly derivative."^[1] LeakyNews review said, "The One with the Sonogram at the End serves mostly to move plot along and give us some character backstory".^[2]

• "The One with the Sonogram at the End" at IMDb