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Abstract |
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Introduction |
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Fertility: based on the distribution of fecundity observed in a `normal' population, normal fertility was defined by the ESHRE Group as achieving a pregnancy within 2 years by regular coital exposure.
Sterility, subfertility, infertility: those couples who do not achieve a pregnancy within 2 years include the sterile members of the population, for whom there is no possibility of natural pregnancy, and the remainder who are subfertile. Together, these comprise the infertile population. The term sterile may refer to either the male or the female, whereas the term subfertile refers to the couple.
Fecundability is the probability of achieving a pregnancy within one menstrual cycle. Fecundity is the ability to achieve a live birth from one cycle's exposure to the risk of pregnancy.
Total fertility rate (per woman) is the average number of children that would be born per woman if all women lived to the end of their reproductive years and bore children, according to the current age patterns of fertility.
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Interactions between reproductive capacity and social changes |
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In the developed world mortality is now almost negligible before the age of 50 years, and breastfeeding is so limited (in incidence and duration) that its effect on fertility is minimal. In many countries marriage is not as frequent as it used to be, but if we take the time of entry into first union, consensual or legal, the mean age when starting conjugal life is not so different from what it was in the past. The consequence of these trends is that the potential number of children a couple might expect if not using any form of family planning is no longer 56, but now around 10. If this number of children were born, there would be a doubling of the population every 15 years, a four-fold increase from one generation to the next.
Changes in the time of childbearing
In fact, couples now have fewer than two children on average in most European countries (Recent demographic developments in Europe, 1999; Macura et al., 2000
). Not only are couples limiting the number of their children, but they also tend to postpone the births to older ages. In France, the mean age at first birth is now over 27 years (for women), roughly 3 years more than 20 years earlier. This new trend has several causes: the lengthening of the period of education, the more frequent entry of women into the labour market, the uncertainties of this market, and the availability of effective contraceptive methods. It is thus unlikely to be reversed in the near future (Leridon, 1999
).
Is fecundity declining?
Therefore, the main reason for low fertility is obviously that men and women want fewer children. Some couples, however, are not able to have the children they would like to have, and the point has been raised whether fecundity is currently declining or not. The issue is made more crucial by the new behaviour shown above: if women tend to postpone childbearing to older ages, they might also face a decline of fecundity due to age. This decline is not easy to assess, because several causes interfere: the risk of spontaneous abortion undoubtedly increases with maternal age (Leridon, 1977), permanent sterility comes well before menopause (Leridon, 1977
; Menken et al., 1986
), and fecundability might also be declining after a particular age. This last point is the more controversial: some analyses based on artificial insemination tend to show that the decline in fecundability starts rather early (after the age of 30 years), but these results cannot easily be extrapolated to natural insemination (Schwartz et al., 1982
).
A possible decline of fecundity over time has been suggested by studies of sperm quality and counts (Carlsen et al., 1992; Auger et al., 1995
; Irvine et al., 1996
), but not everywhere (Bujan et al., 1996
). There is also some evidence of such a trend from demographic surveys, in which individuals are asked about their past fertility and problems in conceiving or childbearing. We must be cautious, however, because couples tend to be more and more impatient when they decide to have a child (Leridon, 1992
), and a recent study has shown that the time to pregnancy is currently declining in Britain (Joffe, 2000
).
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Possible explanations for the very low birth rate |
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To understand the fecundity rates of a population in a given time period, the role of calendar period of birth should be disentangled from that of the mother's cohort. In Italy, for instance, the peak fecundity rate after the second world war was reached around 1965 (2.67/1000 women), as compared with 2.32.4 in the 1950s, and the fecundity rate has been substantially declining since, especially from the mid-1970s onwards. However, an analysis by mother's cohort showed that the mean fecundity rate has been steadily declining for the generations born since 1922, and especially for those born after 1932, in the absence of any appreciable change in trends. Thus, the cross-sectional rates may be strongly influenced by the composition of the different cohorts, and their reproductive pattern (Sorvillo, 1997b; IARC, 1999
).
The most likely possible reasons for the declining birth rates in most European countries are clearly social and economic rather than medical, since no clear correlation can be made between availability and practice of contraceptive methods, nor between abortion rates and birth rates (IARC, 1999). Thus, countries like Italy or Spain, with relatively low frequency of use of oral contraceptives and other contraceptive methods in the past, as well as relatively low and declining abortion rates, also have very low birth rates. In the same way, at least within the ranges observed within the European Union, there is no clear correlation between age at first marriage and fecundity rate. For example, age at first marriage was around 2627 years in Italy or Spain, with very low birth rates, but around 29 years in Denmark, Sweden and Iceland, with appreciably higher birth rates. In all eastern Europe, the mean age at first marriage was as low as 22 years, but fecundity rates were still around or below 1.5 (Annuario Statistico Italiano, 1998
, 1999
).
Thus, neither medical nor demographic factors are correlated with or explain fecundity rates in a satisfactory manner. The interpretations must, therefore, be found essentially in economic but mainly social determinants, since again no clear correlation is observed between GNP and fecundity rates. Some of the differences observed in different countries may be due to different immigration patterns, since immigrant populations tend to have higher birth rates. This may explain the higher fecundity rates in central and northern Europe than in Mediterranean countries, in which immigration has been a more recent and numerically limited phenomenon.
The cohort patterns indicate, in any case, that the decline in birth rates for Europe has been long-lasting, and shows no clear sign of levelling off.
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Economic issues in human reproduction |
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Then as development progresses, mortality rates declinethus allowing more children to survive to adulthoodbut at the same time couples' `demand' also declines because the net benefit of having children falls with urbanization, the introduction of schooling, and the growing availability of other forms of `old-age security'. At this point couples begin to practice deliberate fertility control, and economists' models become relevant. Therefore the focus will be on economic factors that are thought to be relevant in determining the level of fertility after a society has reached the potential `replacement level', of ~2.1 children per woman.
Economic factors influencing post-transitional fertility
For a time it was thought that economic models might be unnecessary in modern societies: perhaps fertility would reach replacement level and then simply remain at about that level. However, the post World War II baby boom in many Western nations, and then the subsequent baby `bust' that has brought fertility rates to as low as 1.2 in some countries, disabused economists of that notion.
Two competing but to some extent complementary theories, developed largely with respect to US experience, are generally referred to in explaining the baby boom and bust in the second half of the twentieth century. One, the `price of time' model, juxtaposes the desire for children, which is assumed to be positively related to family income, with the price of time spent in caring for children, and emphasizes the importance of women's labour force participation and their wages relative to men's in determining that price (Butz and Ward, 1979; Becker, 1981
). It is hypothesized that during the postwar 1940s and 1950s men's wages rose more rapidly than women's, as women were displaced by men returning from the military, so that the price of children fell relative to families' ability to support them, encouraging a baby boom. This situation was assumed to have reversed itself in the late 1960s and into the 1970s as labour market opportunities for women increased and pushed up their wages, leading to an increase in the relative price of children and hence the baby bust.
The competing theory, usually referred to as the `relative cohort size' hypothesis, also assumes a positive relationship between the desire for children and family income but juxtaposes this with a couple's material aspirations, which are assumed to be strongly influenced by the standard of living experienced by young adults when they were growing up (Easterlin, 1987). A couple feels able to afford children only if family income surpasses some threshold determined by material aspirations. It is hypothesized that young adults in the 1950s, who were born and raised in the depression and war years, set a lower threshold on average than young adults in the 1960s and 1970s, who were raised in the affluent postwar years. Compounding this effect of changing tastes, young adults in the 1950s were members of a very small birth cohort (product of the 1930s baby bust) relative to the size of the rest of the labour force, so that their wages were driven up relative to those of older workers in their parents' generation (Welch, 1979
; Macunovich, 1999
). The result was higher wages relative to their own (already low) material aspirations, making children appear very affordable. The large baby boom cohorts had the opposite experience when they entered the labour force, leaving them with reduced wages relative to inflated aspirations, and the baby bust resulted.
Recent work suggests that a model combining these two theories can be used to explain the path of fertility in the USA both before and after 1980 (Macunovich, 1996). The model suggests that the sharp rise in women's wages that occurred in the late 1960s and early 1970s, unique to the USA, actually `buffered' that country from the extremely low fertility rates observed in other Western nations in recent years. Women's wages became an important source of family income during that period when relative male income was low, so that they had a positive effect on fertility rates (Figure 1
).
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The current relative economic situation of young adults in Italy and Spain, who often feel unable financially to set up households independent of their parents, despite growth in the economy generally, suggests that this might be a very significant factor in those countries' current low fertility rates.
The other important economic factor affecting fertility today is the female wage. Young women's wages exert both a (negative) `price of time' and a (positive) income effect on fertility, and the strengths of these two effects vary depending on young men's relative income and on the availability and acceptability of purchased child care. When relative income is high, female labour force participation tends to be lower and the negative `price of time' effect dominates, but when relative income is low, female labour force participation increases as young couples try to supplement their income and increasing proportions of young women remain single; in this case the idea of purchased child care tends to become more acceptable and the `income' effect of women's wages dominates.
This dominant income effect of women's wages appears to have influenced the path of fertility in industrialized countries since about 1985. Many of these countries experienced a `baby boomlet' after 1985, when fertility rates rose appreciably, and recent analyses suggest that during this period fertility rates and women's wages moved in parallel. That is, fertility rates increased most in those countries where female labour force participation rates were highest and female unemployment rates were lowest. This suggests that (i) there is a continuing `demand' for children; (ii) women feel increasingly comfortable with purchased child care; and (iii) they are more able to take advantage of purchased child care as their own earning potential rises.
Psychological aspects
`Why do people want children?' The answer is not simple. The various theories will be considered together with the empirical evidence in support of each perspective, where there is such evidence (Robinson and Stewart, 1989). The motivations for parenthood among infertile couples and single women will also be examined in order to shed further light on this issue.
Explanations for the desire to reproduce have generally been either biological in nature, psychoanalytic, or associated with social pressure. More recently, developments in attachment theory have led to a different approach that focuses on the security of a person's attachment relationships.
Biological explanations
It is often assumed that women's desire to have children is genetically or hormonally based, i.e. because of their capacity to have children, women are biologically predisposed to wish to reproduce. This issue has been addressed by studying individuals with an atypical genetic pattern, or who were exposed to abnormally high or low prenatal sex hormone concentrations. If, for example, women with Turners syndrome (females with an XO genetic pattern), or women who had been exposed to abnormally high concentrations of androgens prenatally (women with congenital adrenal hyperplasia), are found to be less likely to wish to have children, then sex chromosomes or prenatal androgen levels, would appear to be influential in women's desire to reproduce. There is no evidence for either a genetic or hormonal basis to women's motivation to become mothers.
Psychoanalytical explanations
From a traditional psychoanalytical perspective, motherhood is viewed as essential for women's development of a female identity. According to Freud, the successful resolution of the Oedipal conflict for girls involved substituting the desire for a penis with the desire for a baby. Entrenched in traditional psychoanalytical theory is the idea of the `maternal instinct', i.e., women's inborn need to procreate (Deutsch, 1945). For Deutsch, motherhood was considered to be essential in order for women to achieve a sense of fulfillment. Although some psychoanalytic theorists disagreed with Freud's views on penis envy (Horney, 1967
; Thompson, 1967
), motherhood remained closely tied to the development of a female identity. An influential reformulation of the psychoanalyical perspective (Chodorow, 1978
) posited that women become mothers as a result of their experiences with their own mother throughout childhood. However, Chodorow also believed that biological differences between the sexes are at the root of women's desire to reproduce. It was not until the advent of the women's movement in the 1960s and 70s that the idea of the `maternal instinct' as a biologically-based drive, and the importance of motherhood for female identity, were rejected as explanations for women's decision to procreate. Interestingly, this was also the beginning of a new era for women; the introduction of the contraceptive pill meant that, for the first time, women were able to control their fertility.
Socio-cultural explanations
The view that women's desire for children is a function of socio-cultural factors took precedence over psychoanalytical and biological explanations in the latter part of the 20th century. It has been argued not only that women obtain approval for having children (Leiffer, 1980) but also that childlessness is viewed as a form of deviant behaviour, and that those who do not have children, particularly childless married women, are stigmatized by society (Miall, 1989
). In recent years, a number of empirical studies of women's reasons for wanting to have children have been carried out. Of particular interest have been studies of women undergoing infertility treatment, and of single women who have become pregnant through donor insemination, as these women have made an active decision to have a child. In one study (Balen and Trimbos-Kemper, 1995) it was found that women's motivations were strongly associated with the expectation that motherhood would bring happiness, a sense of fulfilment and a secure adult identity.
Attachment relationships
A burgeoning of interest in adult attachment relationships, i.e. the extent to which adults feel secure in their relationship with their own parents, has begun to shed light on why some people are more motivated to have children than others. Attachment relationships are generally categorized as secure, avoidant (when attachment relationships are dismissed as having little importance and intimacy is not expected) or ambivalent (when unresolved conflicts with parents are still ongoing and there is a preoccupation with unfulfilled intimacy needs). In some studies (Rholes et al., 1995, 1997
) it was found that avoidant adults were less interested in becoming parents than secure or ambivalent adults suggesting that a person's history of attachment relationships influences the desire to have a child of his or her own.
There are no clear answers to the question of why women, and to a lesser extent men, wish to have children. However, a substantial proportion of women who attend infertility clinics are at risk of developing clinical depression if their treatment is unsuccessful. This tells us that whatever the reasons for wanting a child, the desire to be a mother is of central importance in many women's lives.
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The role of family planning |
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As an important practical follow-up, in the context of the Tokyo declaration, the Family Planning Associations of the World (Dennis, 1987) pledged to take a series of measures to reduce `the appalling toll of sickness and death caused by unplanned pregnancies', such as to: spread awareness of optimum conditions for childbearing; launch campaigns in each country to ensure that family planning is recognized as an essential component of primary health care; discourage pregnancy before the age of 18; promote spacing of births at least two years apart as an essential life-saving measure; further reduce infant mortality by giving advice and services to mothers and fathers in order to limit family size; counsel parents to cease childbearing after a woman has reached the high-risk age of 35; work within the national, legal and cultural framework to reduce the incidence of illegal abortion; and act without delay to help combat the spread of AIDS through education and appropriate services.
In 1951 the Government of India, for the first time in history, established a national family planning programme. By the 1990s, 155 of 179 governments provided direct, or indirect, support to such programmes and access to contraceptives was limited in two countries (Saudi Arabia and the Vatican State) (United Nations, Population Division, 1998) (Table I
).
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The percentage of couples using any method worldwide, is 58% and the percentage of users employing modern methods (including sterilization, the pill, IUDs, injectables, implants, condom and vaginal barrier methods) is 87%. In the more developed regions (Australia, New Zealand, Europe, Japan and Northern America), these percentages are 70 and 74% respectively, and in the less developed regions, 55 and 91%, respectively (United Nations, Population Division, 1999).
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Estimating the real prevalence of subfertility in an affluent Western society |
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Snick and co-workers (1997), in the Walcheren follow-up study presented data collected for 726 couples in the course of a 9-year review period of primary fertility care in the only hospital of a geographically isolated area of The Netherlands (Snick et al., 1997). The 726 couples represent 10% of the Walcheren population seeking medical care for subfertility problems at least once during their reproductive life span. Strict diagnosis and treatment protocols were adhered to, and only evidence-based treatment was instituted. If no such treatment was available for the couple under consideration, they were counselled extensively on the findings instead. Management was expectant in such cases. This allowed for the calculation of the baseline pregnancy prognosis in untreated subfertility couples from a representative population in a developed country. The couples described in this study had a shorter duration of infertility (mean 21 months) than in most published studies, which may be explained by the fact that most other studies considered patients from referral institutions, whereas Snick's patients visited the Walcheren hospital for their initial fertility work-up. Given the short lines of communication between general physicians and specialist care providers in Walcheren, the regional organization of fertility care, and the demographic characteristics of the population in their investigation, the authors propose that their study reliably reflects baseline fertility prognosis in untreated couples (Table III
). The baseline prognosis in their primary care study is much better (two year cumulative live birth rate 41.9%) than the one calculated from secondary and tertiary care populations (e.g. 21.2% in the CITES study) (Collins et al., 1995
), reflecting different compositions of the respective study populations, notwithstanding their identical inclusion criteria of subfertility. When applying models, this difference should impact on the decision about when to resort to assisted reproduction.
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Availability and uptake of profertility programmes |
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Uptake of infertility services
The current prevalence of infertility in Western and developing countries is ~10% of married and co-habiting couples in which the female partner is aged 1544 years, as indicated above (Zarger et al., 1997; Sundby et al., 1998
). Since females aged 1544 years comprise ~20% of the population of developed countries, 2% of a given country's population are infertile female partners. Thus the current prevalence of infertility is one infertile couple for every 50 individuals in the population (or 20 000 per million population).
Women who seek help for fertility problems are older, have a higher income and are more likely to be married than infertile women who do not (Chandra and Stephen, 1998). Nevertheless, the distribution of occupations among those attending tertiary care infertility centres is typical of the distribution in the population (Collins et al., 1994
). In five European countries, the proportion of infertile couples seeking medical attention ranged from 19% in Poland to 61% in Denmark (Olsen et al., 1996
). The uptake of clinical services by infertile couples in four other surveys averaged <50% of those with infertility (Templeton et al., 1990
; Schmidt and Munster, 1995
; Chandra and Stephen, 1998
; Sundby et al., 1998
). Estimating that 50% of infertile couples seek medical care services, that is equivalent to 5000 couples seeking care for current infertility per million population.
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Need for IVF services |
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Availability of IVF services |
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IVF/ICSI centre density ranged from 0.013.6 centres per million population. The outlying density countries were China, Indonesia, Pakistan, Egypt, India, Poland, Kazachstan and Thailand with fewer than 0.1 reported centres per million and Iceland with one centre and 0.276 million population (3.6 centres per million). The majority of countries in Western Europe, the USA and Australia/New Zealand, however, report one to two IVF/ICSI centres per million population. Israel, Denmark, Finland, Greece and Belgium report more than three IVF/ICSI centres per million population.
IVF/ICSI centre density was higher in countries with low infant mortality rates, which are an indicator of high-quality health services. Even so, two centres per million population would be required to provide IVF/ICSI cycles for more than 750 infertile couples each per annum to meet the needs of the 1500 couples with current infertility and standard indications for IVF and ICSI or persistent infertility.
The number of IVF/ICSI cycles per annum was reported for 35 of the 45 countries having IVF/ICSI centres. Ten had fewer than 100 IVF/ICSI cycles per annum per million population, seven had 100200 cycles, nine had 200500 cycles, eight had 5001000 cycles and Israel reported more than 1600 IVF/ICSI cycles per annum per million population. The number of cycles per million population correlates with the level of public funding for health services. Only Israel appears to have approached the level of IVF/ICSI services that would be sufficient for the 1500 couples with current infertility per million population.
Cost of IVF services
The cost of a single IVF/ICSI cycle has been reported from 24 countries (Fluker and Tiffin, 1996; Golombok et al., 1996
; Phillips et al., 2000
). In 18 of the 24 countries a single IVF/ICSI cycle cost >25% of the gross domestic product per capita. The exceptions were Ireland, the Netherlands, Japan, Norway, Sweden and the UK. IVF/ICSI cost did not contribute significantly to the variability in IVF/ICSI cycles per million among the countries, possibly because IVF/ICSI cost is high relative to income in all countries. IVF/ICSI costs tended to be lower in countries with a higher proportion of public spending on health.
Summary
IVF/ICSI services, which indicate the presence of a full range of infertility treatment services, are available in only 45 countries with 78% of the world population. Moreover, in nearly all countries with such services there is an insufficient supply of IVF/ICSI services to meet the estimated needs of couples with appropriate indications.
One reason for the insufficient level of service is the high cost of IVF/ICSI cycles. Access to IVF/ICSI services is limited to the well-off in many countries and the limited number of cycles in many clinics precludes savings that might be associated with higher service volumes.
Higher levels of public funding for health are associated with higher levels of IVF/ICSI service and lower IVF/ICSI cycle costs.
In some European countries IVF/ICSI births contributed 12% of the total births. In countries in which there is public concern about falling fertility rates, increased levels of IVF/ICSI services through public funding would serve as one way to face these declining rates.
The resources available to treat infertility should be directed more toward the appropriate use of IVF/ICSI services and less toward ineffective treatments.
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Notes |
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1 To whom correspondence should be addressed: Department of Obstetrics and Gynaecology, University of Milano, Via Commenda 12, 20122 Milan, Italy.
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