Robert G. Potter

Fertility, Biology, and Behavior: An Analysis of the Proximate Determinants

Fertility, Biology, and Behavior: An Analysis of the Proximate Determinants presents the proximate determinants of natural fertility. This book discusses the biological and behavioral dimensions of human fertility that are linked to intermediate fertility variables. Organized into nine chapters, this book begins with an overview of the mechanisms through which socioeconomic variables influence fertility. This text then examines the absolute and relative age-specific marital fertility rates of selected populations. Other chapters consider the trends in total fertility rates of selected countries, including Colombia, Kenya, Korea, Indonesia, Mexico, Pakistan, France, and United States. This book discusses as well the effects of deliberate marital fertility control through contraception and induced abortion. The final chapter deals with the management of sex composition and implications for birth spacing. This book is a valuable resource for reproductive physiologists, social scientists, demographers, statisticians, biologists, and graduate students with an interest in the biological and behavioral control of human fertility.

Application of life table techniques to measurement of contraceptive effectiveness

ResumenDos problemas van asociados con el uso efectivo de anticonceptivos. Primero, parejas que pertenecen a una muestra de practicantes, varían típicamente de acuerdo con la probabilidad mensual de fracaco del método. Segundo, no es posible observar a muchas y posiblemente a la mayoría de ellas el tiempo que pueden estar protegridas por el anticonceptivo, porque o suspenden su uso para un embarozo planeado, o se interrumpe la observación por pérdida de contacto con la pareja; puede haber también suspensión del uso por otras razones o se puede descontinuar el estudio de observación. Por estos problemas—Uamémoslos heterogeneidad de la muestra e historias incompletas—se sostiene que la tasa de embarazos de Pearl, que ha sido tradicionalmente usada para medir la anticoncepción es inadecuada.Un método similar al de construcción de tablas de vida se describe aquí, el cual permite la combinación de historias completas e incompletas con el propósito de estimar proporciones en las mujeres de la muestra que pudieron haber permanecido protegridas durante periódos específicos si todos los miembros de la muestra hubieran permanecido bajo observación en dichos períodos. La versatilidad del sistema es ilustrada con una encuesta retrospectiva, en donde se describe el procedimiento detalladamente. Finalmente, se muestra que sólo en condiciones específicas que raramente se encuentran en la práctica, es posible estimar los resultados de nuevas técnicas con el solo conocimiento de las tasas dePearl.SummaryTwo problems are associated with the analysis of use-effectiveness of contraception. First, couples belonging to a sample of contraceptors typically vary in their monthly chances of contraceptive failure. Second, one does not observe for many, and perhaps a majority of the couples, how long they can remain protected with the contraceptive, because either they are stopping contraception to plan a pregnancy or else observation of them is being interrrupted by lost contact, by discontinuation of contraception for other reasons, or by the end of the study. It is argued that because of these two problems—namely, sample heterogeneity and incomplete histories-the Pearl pregnancy rate, which has been traditionally used to measure contraceptive effectiveness, is inadequate.A life table method is described that permits one to combine incomplete histories with complete ones for purposes of estimating the proportions of the sample that might have remained protected for specified periods if all members had remained under observation for these periods. The versatility of the techniques is illustrated in relation toa retrospective survey. A detailed account of procedure is given. Finally, it is shown that only under specialized conditions that are rarely met in practice is it possible to estimate the results of the new technique from knowledge of Pearl pregnancy rates alone.

First ovulation after childbirth: The effect of breast-feeding

Abstract The first postpartum ovulation was diagnosed by means of endometrial biopsy, basal body temperature, vaginal cytology, and cervical mucus in a group of 200 women. The date in which the first postpartum ovulation and the first menstrual flow occurred was analyzed against the nursing status. One hundred and seventy women underwent a natural evolution of nursing; 24 of them ovulated while on full nursing; 49, while on partial nursing; and 97, when nursing had been discontinued. In 30 women, nursing was artificially suspended immediately after delivery. No women ovulated before the thirty-sixth postpartum day in the entire study group. The intensity and length of nursing affected the date in which the first postpartum ovulation occurred. The first postpartum menstruation was ovulatory in 78 per cent of the patients. Twelve pregnancies started with the first postpartum ovulation. Our data indicate that besides the re-establishment of ovulation other factors could be involved in the recovery of fertility after childbirth.

Postamenorrheic versus postpartum strategies of contraception

The postpartum strategy of inserting an intra-uterine device shortly after a birth essentially eliminates the risk of conceiving again before starting contraception but maximizes the overlap between wearing time and postpartum anovulation when protection is not needed. In contrast, the postamenorrheic strategy of delaying insertion until right after the woman’s first menses all but removes overlap with anovulation but allows a chance of conception before start of contraception because sometimes an ovulation precedes the first menstruation.In this paper some algebra is developed and utilized to see which of the two strategies delays the next conception longer. The postamenorrheic strategy is found to have a slight advantage over the postpartum approach for a wide range of fecundability levels, lengths of anovulation, and rates of continuation of IUD. However this slight advantage presupposes that insertions are taking place at the exact time prescribed. When a progressively larger factor of procrastination is introduced, the advantage rapidly passes from the postamenorrheic to the postpartum approach. An explanation for the differing sensitivity of the two insertion strategies with respect to procrastination is derived from the results of an earlier analysis.

A computer model of family building based on expected values

ResumenSe describe un modele de probabilidad (calculado por medio del computador electrónico) del crecimiento familiar, llamado FERMOD. El modelo es diseñado para seguir la cambiante distribución de niños nacidos vivos y los intervalos entre nacimientos de una gran población homoqénea cuando se mueve a través del período reproductivo. El uso del modelo hace algunos supuestoe acerca de [actores tales como riesgos del desgastefetal, longitudes de embarasoe y amenorrea post-partum condicionada al resultado del embaraso, longitud del periodo reproductivo, fertilidad, tamaño deseado de la familia, espacio preferido entre nacimientos, y efectividad de los métodos anticonceptivos. El uso de FERMOD es ilustrado en una limitada aplicación a la fertilidad en los Estados Unidos, Se discuten brevemente las relaciones con otros modelos.SummaryA computerized probability model of family building is described. Called FERMOD, the model is designed to follow the changing distribution of children ever born and birth intervals of a large homogeneous population as it moves through the reproductive period. Use of the model presupposes assumptions about such factors as risks of fetal wastage, lengths of pregnancy, and postdelivery amenorrhea conditional to outcome of pregnancy, length of reproductive period, fecundability, desired family size, preferred birth spacing!, and effectiveness of contraception. Use of FERMOD is illustrated in a limited application to United States fertility. Relations to other models are briefly discussed.

Fertility effect of seasonal migration and seasonal variation in fecundability: test of a useful approximation under more general conditions.

A demographer J. Menken recently demonstrated that the asymptotic birth rate calculated by a family-building model for a population with seasonal variation in fecundability due to such causes as seasonal separation of spouses is close to the birth rate of a population in which fecundability is kept constant at the mean of the seasonally varying values. This theory was tested and proven with a set of complex fertility simulations. Results hold up well for various combinations of numbers of months of annual separation. These findings are important for demographers because it seems that seasonally varying fecundability can be allowed for without simulating this variation directly in family-building models.

Selective fecundability and contraceptive effectiveness.

A study based on an extended model using the Type I-geometric distribution fitted by Jain to a sample of 2190 Taichung women was conducted to confirm Tietzes findings that in the absence of contraception the fecundability composition of a group of women changes rapidly by a selective process whereby more fecund women become pregnant leaving behind an increasingly subfecund group. Tabulated results show that the process becomes progressively slower with increasingly effective contraception. Mean values of fecundability are given according to effectiveness of contraception and months of fecundable exposure without pregnancy. The proportion of women accidentally conceiving within 2 years of contraceptive use decreases with increasing contraceptive effectiveness and with the length of preceding period of nonprotection during which the proportion of subfecund women is increased. After 4 years of nonprotection the rate of accidental pregnancy is reduced by a factor of 3. Potential sources of bias facing any comparison of contraceptive methods such as unequal length of observation of women using various methods and amount of overlap or interval between time of contraceptive initiation and amenorrhea are discussed with respect to family planning programs. IUD effectiveness for different age groups of women (under 24-39) in Taichung is discussed. An extensive appendix describes mathematical details relating to the model.

Some effects of spouse separation on fertility.

Simple probability models incorporating an approximation first demonstrated by Menken (1979) are used to study births averted by two classes of temporary spouse separation, single and cyclic, under conditions of natural fertility. For either class of spouse separation, births averted increases disproportionately with longer separation. For a given length of separation, births prevented are more sensitive to change in length of anovulation than to change in level ofnatural fecundability or risk of spontaneous abortion. In addition, by means of the macrosimulation model REPMOD (Bongaarts, 1977), it is shown that the fertility impact of temporary spouse separation tends to decrease as couples age.

Competition between spontaneous and induced abortion

Because of their similar timing in pregnancy, spontaneous and induced abortions can be viewed as competing outcomes. Some intended abortion operations are anticipated by earlier miscarriages while some potential miscarriages are forestalled by earlier deliberate interruptions of pregnancy. Previous treatments of this competition are reviewed, and a new analysis is made on the basis of New York data. A simple rule for approximating the reduction in apparent incidence of spontaneous abortion in the presence of induced abortion is presented. The effects of nonreporting and misreporting of pregnancy outcomes upon this rule are examined by means of the Perrin-Sheps renewal process. Two expectations are tested on Taiwanese data.

Family Planning and Fecundity

Abstract A computerized probability model of family-building, FERMOD, is described and then utilized in an investigation of relations between family planning and fecundity as applying to white couples of the contemporary United States. Models of this type that formulate reproductive performance as a stochastic process permit one to explore relations that are not directly observable and in this manner to secure at least partial answers to questions not subject to investigation by survey research alone. Two main questions are addressed concerning the dependence of family planning success upon fecundity: (1) How quickly does spacing control deteriorate when natural fecundability is taken at progressively lower values or when the risk of pregnancy wastage is set at progressively higher values? (2) What is the distribution of unsought births among couples of average fecundity when they practise contraception with specified effectiveness and have stipulated spacing and family size goals?