By the time the "Majin Buu Saga," which was the franchise's next instalment, rolled around, seven years had passed and Chi-Chi had given birth to their second son, Goten. This means Goten was likely conceived during the period right before the Cell Games when Goku was almost permanently in his Super Saiyan form.

How was Gohan conceived?

He was conceived by a Super Saiyan, in Super Saiyan form.

How was Goten conceived if Goku was dead?

Goten is born nine months after the defeat of Cell in the Cell Games Saga. As Goku died during the Cell Games, while Chi-Chi was pregnant, Goten did not meet his father Goku until he reached the age of seven. ... Goten transforming into a Super Saiyan made him the youngest Super Saiyan ever at that point.