INSERT_TITLE_0 Materials and Methods

1. Introduction

In healthy non-contracepting sexually active couples fecundability, probability of conceiving a pregnancy during a menstrual cycle [Gini 1924, Gini 1928], depends on behaviour as well as physiology. Spermatozoa with the capability of fertilising the egg must already be present in the woman's reproductive tract at the time the egg is released at ovulation or must arrive there soon after. Number and timing of acts of intercourse in the cycle are an important factor. The width of the "fertile" window around ovulation, that is the number of days during which intercourse has a non-zero probability of resulting in conception, is uncertain. Widely diverging figures have been proposed in the literature, ranging from less than two to more than ten days [Glass and Grebenik 1954, Potter 1961, James 1963, Marshall 1967, Lachenbruch 1967, Glasser and Lachenbruch 1968, Barrett and Marshall 1969, Barrett 1971, Loevner 1976, Vollman 1977, Schwartz et al 1979, Trussell 1979, Schwartz, MacDonald, and Heuchel 1980, Royston 1982, Bongaarts and Potter 1983, World Health Organization 1983, World Health Organization 1985, Potter and Millman 1985, Bremme 1991, Weinberg, Gladen, and Wilcox 1994, Trussell 1996, Masarotto and Romualdi 1997, Weinberg et al 1998, Wilcox, Weinberg, and Baird 1998, Sinai, Jennings, and Arévalo 1999, Dunson et al 1999]. These estimates depend on data analysed, on conjectures accepted, on evaluations made with different approaches. Precise information on the pattern of daily fecundability and the width and location of the associated fertile interval in the menstrual cycle is of interest to both the biologist and the demographer. For the purpose of fertility regulation, the information is essential to those couples attempting to avoid pregnancy and those trying to achieve this end through appropriate timing of intercourse. The need for a large menstrual cycle data base, including a high number of conception cycles, for the purpose of clarifying various points of interest for basic knowledge and applications, has been repeatedly emphasised [Schwartz, MacDonald, and Heuchel 1980, James 1981, Potter and Millman 1986, Royston 1991, Royston and Ferreira 1999].

This paper introduces the results of an exercise performed in this direction with the co-operative collaboration of a group of organised centres giving advice to subjects interested in learning about the fertile phase of the woman and the use of a Natural Family Planning method to avoid or achieve pregnancies. To reach the planned target number of pregnancies (about 500) with a prospective design in a reasonable amount of time, the participation of several centres was necessary. In the following is given a summary description of the common protocol adopted and of the whole study design. We also describe the characteristics of the study subjects and centres and present preliminary analytical results. These results give special attention to covariates linked with the magnitude and pattern in the daily conception probabilities. They are compared with previous estimates from the literature. Mention is also made on ongoing lines of research opened by the available database.

 

INSERT_TITLE_0 Materials and Methods

Daily Fecundability: First Results from a New Data Base
Bernardo Colombo, Guido Masarotto
© 2000 Max-Planck-Gesellschaft ISSN 1435-9871
http://www.demographic-research.org/Volumes/Vol3/5