Women who become pregnant through IVF may be more likely to develop life-threatening blood clots, researchers have warned. The study, the first of its kind, found that their risk rose fivefold in early pregnancy compared with women . Is it safe to have sex when I'm pregnant? Most women who are having a normal pregnancy may continue to have sex right up until their water breaks or they go into labor. There are some circumstances, though, in which you may need to modify your activity or abstain from sex altogether for part or all of your pregnancy. Sex differences in human physiology are distinctions of physiological characteristics associated with either male or female humans. These can be of several types, including direct and indirect. Direct being the direct result of differences prescribed by the Y-chromosome, and indirect being a characteristic influenced indirectly (e.g. hormonally) .