I was thinking about how the aliens in my generation ship story sterilize people that have a genetic disease but don't sterilize carriers. The complete spermicide for males makes perfect sense. But with females, it is more complicated. What complicates things with females? The menstrual cycle of course. What I am aiming for is a way to inhibit ovulation without also inhibiting menstruation. So I looked at graphs of the menstrual cycle and the hormones and thought that since LH is the 1 hormone that triggers ovulation in the first place, an LH inhibitor would stop ovulation from happening at LH levels that would normally trigger ovulation. And because it is not estrogen or progesterone(both of which stop periods and estrogen, if taken at the right time can actually act as a natural fertility drug, raising the chances of having twins and higher order multiples), those 2 hormones should still cycle as normal with dips corresponding to menstruation. So basically, ovulation has stopped but there is still a menstrual cycle. But could a direct inhibitor of LH stop ovulation without stopping periods? Or would it have the same amenorrhea effects as estrogen and progesterone do along with the direct effect of anovulation? I know lots of people say ovulation is essential to have periods but I don't think that is true. Every woman has at least 1 anovulatory cycle in her lifetime but menstruation continues on. Menarche is an example of failed ovulation triggering a period. And likewise, some women have cycles where they ovulate without having a period. Most of that is related to pregnancy and breastfeeding but even women like me who have never been pregnant or breastfed sometimes have ovulation without a period. So, yes there is a strong correlation between ovulation and periods but just like menarche is triggered by a fail to ovulate(at least that is the way it is for lots of women), I think an LH inhibitor would cause ovulation to fail despite the LH surge and thus trigger a period like the failed ovulation that triggers menarche.