Though related, the terms gender and sex do not always mean the same thing. Gender often focuses more on the internal, using the terms masculine and feminine. Sex often focuses on the external, using the terms male and female. In other words, gender relates greatly to the mental and emotional concepts associated to one's physical form, while sex is often used to identify what physical form you take using biological references.
A man's gender often fits the roles one's society or culture deems to be masculine and is of the male sex.
A woman's gender often fits the roles one's society or culture deems to be feminine and is of the female sex.
Haruka's gender and sex has been put to question quite often by fans outside of Japan. Some of this is due to information lost in translation. Another reason is due to the anime under going censorship in dubs created by various outside countries.
In the original manga, it is stated by Sailor Neptune to Princess Serenity, "Princess, Uranus is like a man and woman in one. She has the strengths of both genders. It is her special advantage as a soldier."
While for some that can be confusing, in America during the 1990s TokyoPop translated it as, "Princess... Uranus is... both a girl and a guy. She has the strengths and the personalities of both genders."
It is hard not to be confused, if not completely misled, by such a translation. In result, many fans questioned what Haruka's sex was. Was she really a man? Was she a man who could turn into a woman or was it the other way around? Was she a hermaphrodite?
The debate on her sex was officially answered in 1998 at the San Diego Comic Con. Naoko Takeuchi took part in the convention in August that year and on one of the days she participated in a one-hour question and answer panel.
While a full documentation of the interview is not available articles on the event have appeared in two magazines over the years. In the TokyoPop magazine Smile a article on the event was documented in its December 1998 issue. It featured questions and answers that fell more towards the general scale of Sailor Moon topics, leaving out all mention of Sailor Uranus and Sailor Neptune.
Fortunately, Animerica's monthly magazine contained an article that did address the questions and answers on them. In the 1998 Volume 6.11, though not in interview form, the questions and answers given at the panel are featured. The question of Haruka's gender came up at the event and Naoko Takeuchi replied, "All the Sailor Soldiers are girls. Haruka has always been a girl and always will be."
Ultimately, Haruka's gender is both masculine and feminine. Her sex is female.
Sources:
San Diego Comic Con Interview. Animerica Magazine Volume 6.11. San Francisco, CA: Viz Media. 1998.