Editing Calendar-based contraceptive methods (section)

===Knaus–Ogino or rhythm method===
In 1905 [[Theodoor Hendrik van de Velde]], a Dutch gynecologist, showed that women only ovulate once per menstrual cycle.<ref>{{cite web | title=A Brief History of Fertility Charting | work=FertilityFriend.com | url=http://www.fertilityfriend.com/Faqs/A_brief_history_of_fertility_charting.html | access-date=2006-06-18}}</ref>  In the 1920s, [[Kyusaku Ogino]], a Japanese gynecologist, and Hermann Knaus, from Austria, working independently, each made the discovery that ovulation occurs about fourteen days before the next menstrual period.<ref name="singer">{{cite book |first=Katie |last=Singer |year=2004 |title=The Garden of Fertility |publisher=Avery | location=New York | isbn=1-58333-182-4 |pages=226–7}}</ref> Ogino used his discovery to develop a formula for use in aiding infertile women to time intercourse to achieve pregnancy.<!-- This if from the Japanese article on Ogino (as best I could tell from the internet translator I used), but that page does not cite its sources -->

In 1930, Johannes Smulders, a [[Roman Catholic]] physician from the Netherlands, used Knaus and Ogino's discoveries to create a method for ''avoiding'' pregnancy. Smulders published his work with the Dutch Roman Catholic medical association, and this was the official rhythm method promoted over the next several decades.<ref name="singer" /> In 1932 a Catholic physician, Dr. Leo J Latz, published a book titled ''The Rhythm of Sterility and Fertility in Women'' describing the method,<ref name="wife">{{cite book | first=Marilyn | last=Yalom | year=2001 | title=A History of the Wife | edition=First | publisher=HarperCollins | location=New York | isbn=0-06-019338-7 | pages=[https://archive.org/details/historyofwife00mari/page/297 297]–8, 307 | url-access=registration | url=https://archive.org/details/historyofwife00mari }}</ref> and the 1930s also saw the first U.S. Rhythm Clinic (founded by [[John Rock (American scientist)|John Rock]]) to teach the method to Catholic couples.<ref>{{cite magazine |last=Gladwell |first=Malcolm |title=John Rock's Error | magazine = The New Yorker |date= 2000-03-10 }}</ref>