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Papers

The timing of the “fertile window” in the menstrual cycle: day specific estimates from a prospective study

BMJ 2000; 321 doi: https://doi.org/10.1136/bmj.321.7271.1259 (Published 18 November 2000) Cite this as: BMJ 2000;321:1259

Rapid Response:

Why bother with calendar rhythm when prospective fertility markers are available?

Wilcox, Dunson & Baird rightly show that calendar rhythm is
unreliable. That is why the prospective marker of the cervical mucus,
which accurately reflects the plasma oestrogen level when it passes a
woman's threshold (see J.M. Brown's work for WHO, for example [1][2][3]) is the reliable
marker used in the Billings Ovulation method and all reliable
symptothermal methods. The most recent Billings study by Qian (China)
found 0 method related, and 0.51% user-related pregnancies in 963 couples
using the method for 1 year.

By all means, let's bury calendar rhythm - honorably, but let's bury
it.

Hanna Klaus, M.D.
8514 Bradmoor Drive
Bethesda, MD 20817-3810, USA

Hanna Klaus, M.D., F.A.C.O.G. is the Executive Director of the Natural
Family Planning Center of Washington, D.C., She has published
use-effectiveness studies of the Billings Ovulation Method, currently
serves as medical consultant to the Billings Ovulation Method Association
of the USA. She was formerly Associate Professor, and later Clinical
Associate Professor of Obstetrics and Gynecology at the George Washington
University Medical Center, Washington, D.C., and consultant to the U.S.
Agency for International Development for natural family planning and
adolescent sexuality and fertility.

Billings EL, Billings JJ, Brown JB, Burger H: Symptoms and Hormonal Changes
Accompanying Ovulation. Lancet 1972;1:282-5.

World Health Organization: Temporal Relationships between indices of the
fertile period. Fertil Steril 1983;39:647-655.

Blackwell LF, Brown JB, Cooke D: Definition of the potentially fertile
period from unrinary steroid excretion rates. Part II. A threshold value
for pregnanediol glucuronide as a marker for the end of the potentially
fertile period in the human menstrual cycle. Steroids 1998;63:5-13.

Competing interests: No competing interests

21 November 2000
Hanna Klaus
Executive Director
Natural Family Planning Center of Washington, D.C.