In The Left Hand of Darkness, how did the Gethens reproduce?

The field notes of one of the first Investigators, Ong Tot Oppong, describe the androgyny of Gethenians. Their sexual cycle averages between 26 and 28 days. For 21 to 22 days the individual is sexually inactive, or in somer. But by the 23rd day the individual enters kemmer, where the sexual impulse is strong. Only when the subject finds a partner do the hormonal secretions establish one as the male or female, and the genitals change accordingly. This is not set in stone, however. A Gethenian may father several children and be the mother to others. If the partner adopting the female role is impregnated, hormonal secretion continues for the 8.4-month gestation period.