I just came across a discusion of a teshuva in the Igros Moshe by Rav Zilberstein - and he seems to cite it inaccurately First I'll quote his discussion of the issue - and then the relevant excerpt from the Igros Moshe. This is a caution that even such a great talmid chachom occacionly makes errors. It doesn't necessary invalidate the halachic conclusion but it does show that his conclusion can not be learned from the statement of Rav Moshe that he cites. He says that it deals with a married couple that would need to divorce. Rav Moshe in fact is dealing with two people who want to marry and he says that it is significant whether they are married or only contemplating marriage. Secondly the issue involves whether there is a heter for birth control - when there are lenient and stringent view among the rabbis for this situation. Because of danger to the woman Rav Moshe allows the use of the lenient in their case. Thus it would seem that even if it were a condition of pikuach nefesh - if there weren't lenient views - Rav Moshe would not permit birth control. But in his conclusion he prohibits the use of birth control because with total bed rest pregnancy is not dangerous for her condition. The fact that total bedrest for nine months is a very stressful thing does not enter into the evaluation. Thus Rav Zilberstein's statement that pikuach nefesh overrules the entire Torah - is not the view expressed in the Igros Moshe where he doesn't even use the word pikuach nefesh and he gives leniencies only on a very circumscribed basis.
Rav Zilberstein( Assia Nissan 5747): In the Igros Moshe (1:67) concerning a young couple who are so much in love that if their marriage would be ended the woman would be in danger because of her severe upset which is equivalent to a condition of pikuach nefesh. It is also know that a woman who doesn’t have children for 10 years that according to the law of the Torah it is permitted for the husband to divorce her so that he can marry another woman and fulfill the obligation to have children. Nevetheless if there is a real concern that because of being divorced the woman will go into severe depression and danger – then this is pikuach nefesh which overrules the entire Torah.
Igros Moshe(E.H. 1:67):This concerns a 40 year old man who has never had children and he wants to marry a young woman whom he finds attractive and she is Torah observant. This is something which is difficult for him to find. However unfortunately she has kidney disease and therefore according to the doctors it would be dangerous for her to become pregnant at the present time. However at a later time when her condition has improved it would not be dangerous to become pregnant. The question is whether they can get married and have permission to use birth control methods to prevent pregnancy?… However nevertheless if you see that they are so much in love until it would possibly be a danger to one of them if they didn’t get married. In particular the concern is for the sick and weak young lady - who besides that she would not be able to marry him but also there is concern because of her condition that she would be prohibited to marry everyone and thus be in an very unfortunate situation – there is a basis to permit them to marry with birth control. But this is only on the condition that they are modest and reliable with many warnings not to publicize that they received permission [to follow the lenient opinions]. But on the other hand I have heard that if there is total bedrest during the entire pregnancy – there is no danger to a woman who is sick with kidney disease. Therefore in fact there is no permission to use birth control. Rather they should be advised that if she becomes pregnant that she should have total bedrest.