Peter J Flegg,
Blackpool Victoria Hospital, UK, FY3 8NR
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Like your correspondent, Tony Floyd, I am also beginning to entertain doubts about a lot of things, having spent some time appreciating the scientific logic of the HIV dissidents and their "evidence" that HIV is not spread sexually.
I realise that one of the main cornerstones in their argument is the finding by Nancy Padian that HIV transmission occurred infrequently in heterosexual couples (the dissidents conveniently ignore other studies showing higher transmission rates, or refuse to acknowledge the reasons as to why the rate of transmission was low in Padian's study).
I wondered if I could apply the same infallible logic to the thorny issue of whether pregnancy is the result of sexual intercourse. After all, they are not very well correlated temporally, not everyone who has sex becomes pregnant, and there are many cases where pregnancy has occurred when the woman concerned has categorically denied having had sex! These facts are highly suggestive that the outcome event and the putative risk activity are completely unrelated.
I eventually found "proof" for my theory when I read of a study looking at pregnancy rates in heterosexual couples over a study period of 250 couple-years duration(1). This study found very few pregnancy events, and indeed in one part of the study no pregnancies were recorded at all. This reinforces my pre-existing conviction that my theory is right.
However, I am ignoring some relevant facts. These will obviously be important in diminishing the chances of observing a pregnancy event, but I will conveniently choose to ignore them, since as a true neodissident scientist, I will be sure not to let facts get in the way of my opinions.
(1) To be eligible for the study, couples had to have been engaged in a long term sexual relationship that had already failed to be associated with a pregnancy event.
(2) Nothing was known about the couples underlying fertility.
(3) Before, and during the study at 6 monthly intervals, couples were encouraged to practice safe sex and use condoms.
(4) 75% of couples used condoms in the study.
(5) 15% abstained from sex entirely.
I know all of these things would significantly lessen the chance of pregnancy if indeed it is sexually "transmitted", but none of them can shake my conviction that this study above all others provides conclusive proof that sex cannot result in pregnancy.
References (with apologies to Nancy Padian) (1) Padian N, Shiboski S, Vittinghoff E, Glass S. Heterosexual transmission of pregnancy: Results from a ten year study. Am J Epidemiol 146:350-357, 1997
PS - substitute HIV for pregnancy to get the original Padian reference.
Competing interests: None declared