QuestionHI Dr.
I'm reviewing medical articles and for some reason there's inconsistencies between experts on the chances of pregnancy with a single act of intercourse.
Wilcox states that there's 10% chance of pregnancy five days before ovulation, peaking to 33% on the day of ovulation, whereas, a study by Barrett and Marshall has shown that random acts of intercourse achieve a 24% pregnancy rate per cycle.
That study also found that timed intercourse based on information from a BBT-only method of FA increased pregnancy rates to 31%-68%.
Studies of cervical-mucus methods of fertility awareness have found pregnancy rates of 67%-81% in the first cycle if intercourse occurred on the Peak Day of the mucus sign.
A Chinese study of couples practicing random intercourse to achieve pregnancy used very sensitive pregnancy tests to detect pregnancy. It found a 40% conception rate per cycle over the 12-month study period.
The later studies were found by typing "fertility awareness" via Wikipedia.
WHAT IS CORRECT? AND WHY THE INCONSISTENCIES BET STUDIES.
PS- Thank you for spending time answering these questions as they do assist the public in better understanding issues relating to health and well-being.
AnswerHello Jack,
It's an interesting question. I think the answer as to why the inconsistencies is that some studies are better than others, and some studies (or their readers) reach conclusions not warranted by the evidence. For example, in the study of women using peak cervical mucous (reported in the British Medical Journal), they report a rate of 67% pregnancy, but that was a total of 6 pregnancies in 9 women. It's not statistically significant to generalize that to the total population. Some studies make claims, but don't really have the data to support those claims.
The generally recognized rate of conception per cycle when intercourse occurs before ovulation is 20-30%. I can't tell you exactly where those figures came from, but I would guess that those figures are probably fairly accurate.
