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PubMed1997

The effect of child survival on fertility in Zimbabwe: a micro-macro level analysis.

The literature on the effect of fertility on child survival is extensive especially since the accumulation of data from the World Fertility, and Demographic and Health Surveys. Comparatively, empirical studies examining the other side of the relationship--the effect of child survival on fertility--are sparse although theoretical considerations suggest the interdependence of child survival and fertility. Furthermore, the relationship of child survival and fertility is often examined at the micro-level. There is growing recognition, however, that this relationship may be also influenced by macro-level factors. This study attempts to measure the effect of child survival on birth intervals in Zimbabwe using a micro-macro analytical approach based on the individual and community data from the 1988 Zimbabwe Demographic and Health Survey, and the 1989/1990 Zimbabwe Service Availability Survey, respectively. The multivariate analysis showed that there is a replacement effect in the relationship between child survival and fertility independent of individual characteristics of women in Zimbabwe. The analysis also showed that health interventions as measured by coverage and visit by a mobile family planning clinic, and access to a health service have differential impact on fertility in Zimbabwe controlling for the survival status of the previous to the last child and individual characteristics of the women.

Adolescent↗
PubMed2004

Male fertility in natural populations of red deer is determined by sperm velocity and the proportion of normal spermatozoa.

Male reproductive success is determined by the ability of males to gain sexual access to females and by their ability to fertilize ova. Among polygynous mammals, males differ markedly in their reproductive success, and a great deal of effort has been made to understand how selective forces have shaped traits that enhance male competitiveness both before and after copulation (i.e., sperm competition). However, the possibility that males also may differ in their fertility has been ignored under the assumption that male infertility is rare in natural populations because selection against it is likely to be strong. In the present study, we examined which semen traits correlate with male fertility in natural populations of Iberian red deer (Cervus elaphus hispanicus). We found no trade-offs between semen traits. Our analyses revealed strong associations between sperm production and sperm swimming velocity, sperm motility and proportion of morphologically normal spermatozoa, and sperm viability and acrosome integrity. These last two variables had the lowest coefficients of variation, suggesting that these traits have stabilized at high values and are unlikely to be related to fitness. In a fertility trial, our results show a large degree of variation in male fertility, and differences in fertility were determined mainly by sperm swimming velocity and by the proportion of morphologically normal sperm. We conclude that male fertility varies substantially in natural populations of Iberian red deer and that, when sperm numbers are equal, it is determined mainly by sperm swimming velocity and sperm morphology.

Animals↗
PubMed1992

Fertilization failure of frozen mouse oocytes is not due to premature cortical granule release.

The proportion of mouse oocytes that were fertilized in vitro after storage at -196 degrees C in the presence of 1.5 M dimethylsulfoxide (DMSO) was significantly lower than in unfrozen controls (39% vs. 81%). Sperm failed to penetrate the zona pellucida of approximately 80% of the frozen oocytes that remained unfertilized. Removal of the zona restored fertilization to control levels, indicating that changes induced in the zona during freezing and/or thawing were the primary cause of fertilization failure. Sperm-oocyte fusion, sperm nucleus decondensation, and the resumption of meiosis in frozen oocytes appeared to be delayed but subsequently fertilization progressed normally. No evidence was found to suggest zona modification by the premature release of fucosyl-rich glycoconjugates of cortical granule origin onto the surface of the plasma membrane of frozen oocytes stained immediately after thawing with fluorescently labeled Ulex europaeus lectin. Only a few frozen (less than 5%) and control (less than 3%) oocytes that failed to fertilize in vitro had fucosylated molecules on the plasma membrane. Prolonged exposure of fertilized oocytes to DMSO at 4 degrees C did not alter the pattern of lectin binding. In conclusion, fertilization is inhibited in frozen-thawed oocytes by as yet undefined modifications to the zona pellucida which do not involve the premature release of cortical granules.

Animals↗
PubMed1993

Normal fertilization and development of frozen-thawed mouse oocytes: protective action of certain macromolecules.

Freezing and thawing of mouse oocytes causes changes in the zona pellucida that reduce fertilization. The fertilization and development of oocytes were studied after freezing and thawing in media containing 1.5 M dimethylsulfoxide (DMSO) and various macromolecular supplements: BSA (Fraction V and crystalline), fetal calf serum (FCS), and polyvinyl alcohol (PVA). In conditions under which the fertilization rate of oocytes frozen in medium containing BSA was reduced, oocytes frozen in medium containing FCS were fertilized at rates approaching those of nonfrozen controls. Significantly fewer oocytes were fertilized after freezing in the presence of PVA than oocytes frozen in medium containing BSA or FCS. Fertilization of oocytes frozen in the presence of PVA was significantly increased when serum was included in the medium during dilution of the cryoprotectant. The in vitro and in vivo development of embryos obtained from frozen-thawed oocytes was independent of the macromolecular supplement used in the freezing medium and was similar to that of nonfrozen control oocytes. The results show that given the appropriate conditions for freezing and thawing, cryopreserved mouse oocytes undergo fertilization and development at rates similar to those for nonfrozen controls.

Animals↗
PubMed1994

Spermatozoa retention by Sertoli cells during the decline in fertility in aging roosters.

Fertility of domestic roosters peaked and then began a steep decline within the first year of life. The decline was concomitant with a steady reduction in total number of spermatozoa per ejaculate. We found that 1) the decline was neither related to germinal epithelium regression nor to spermatozoa abnormalities, as reported for aging males of nonseasonal breeders and for fertile seasonal breeders during the nonmating period and 2) seminiferous tubules of extremely low-fertility aging roosters contained more Sertoli cell-spermatozoa complexes than did more fertile roosters, which is in sharp contrast to what occurs in other domestic males. We further observed that Sertoli cells of low-fertility roosters had smaller diameters, cytoplasm that stained deeper, and more crowded cytoplasmic inclusions than did Sertoli cells of high-fertility roosters. We conclude that the decline of fertility in aging roosters is related to changes in Sertoli cells that impair the regular release of spermatozoa. Spermatozoa remain within the testicular tubules and thus fewer spermatozoa are available for insemination.

Aging↗
PubMed1998

Recombinant fertilization antigen-1 causes a contraceptive effect in actively immunized mice.

Recombinant (r) fertilization antigen (FA)-1 was investigated for its immunocontraceptive effect using the mouse as a model. Active immunization with the murine rFA-1 antigen raised high antibody titers in all the immunized mice (n = 16 in two trials); these titers were long lasting and reached preimmunization levels by the 255th day. There was a significant (p < 0.0001) effect (64% reduction in trial I and 70% reduction in trial II) in fertility of immunized animals compared to PBS-control animals (n = 22 in two trials). The effect on fertility was reversible. When the antibody titers declined to control levels, all the animals conceived and delivered healthy babies without a significant (p > 0.05) effect on the litter size compared to that of controls. There was a significant (p = 0.025) correlation (r = 0.76) between the reduction in fertility and the circulating rFA-1 antibody titers. Anti-rFA-1 antibodies from immunized mice, and not the immunoglobulins from the PBS-control mice, significantly (p < 0.001) blocked murine sperm binding to zona pellucida and in vitro fertilization of murine oocytes. In a Western blot procedure, the anti-rFA-1 antibodies specifically recognized the protein band of approximately 47 kDa (dimeric form of cognate FA-1 antigen) only in the protein extract of testes and not in the extracts of somatic tissues tested, namely kidney, liver, intestine, spleen, muscle, heart, lung, brain, and ovary. In conclusion, our data indicate that active immunization with rFA-1 antigen induces a strong and sperm/testis-specific antibody response that causes a reversible inhibition of fertility by affecting sperm-zona binding and the fertilization process. These findings suggest that rFA-1 antigen is an exciting candidate for the development of a contraceptive vaccine.

Animals↗
PubMed2000

Fertility diminution in female rats with experimental chronic nephrosis.

Chronic aminonucleoside nephrosis in rats is an experimental analogue of human focal segmental glomerulosclerosis. This study was undertaken to define the effects of chronic nephrosis on the pituitary-ovarian axis and on fertility. Chronic nephrosis was induced by puromycin aminonucleoside and followed for 112 days. The estrous cycle was evaluated daily in all rats, whereas biochemical parameters, hormonal concentrations, and fertility were measured on Days 7, 14, 28, 56, 84, and 112 (n = 8). Animals were divided in four experimental groups: A, B, C, and D. Group A was used to determine LH, FSH, progesterone, and estradiol concentrations. Group B was used to evaluate fertility, and groups C and D were added to clarify the role of male rats in the fertility of nephrotic female rats. The results showed a persistent proteinuria in nephrotic rats; the estrous cycle of nephrotic animals was disrupted. The LH and estradiol concentrations were significantly low at all time points evaluated, whereas no significant changes were noted in FSH or progesterone values. In addition, fertility and litter size were diminished in nephrotic female rats. Interestingly, the presence of a male rat or its urine resulted in a positive influence on serum estradiol concentrations of nephrotic female rats. These data indicate that experimental chronic nephrosis results in a pituitary-ovarian dysfunction that is characterized by low LH concentration, hypoestrogenism, failure of the hormonal feedback control, and diminution of fertility. In addition, they show the positive effect of a male rat on the fertility of a nephrotic female, which strongly suggests the participation of pheromones.

Animals↗
PubMed2000

SFE1, a constituent of the fertilization envelope in the sea urchin is made by oocytes and contains low-density lipoprotein-receptor-like repeats.

At fertilization in most animals, cortical granules of the egg or oocyte secrete their contents, whose function it is to modify the extracellular matrix. This modified matrix then participates in the block to polyspermy and protection for early embryonic development. In the sea urchin, contents of the cortical granules are secreted within 30 sec of insemination. Several of these content proteins then bind to the nascent vitelline layer of the egg and lift off the cell surface to form a stable, impervious, fertilization envelope. At least six major proteins are present in the envelope, and recently we have identified cDNA clones of two, ovoperoxidase, and SFE9. Here we report on the identification and characterization of SFE1, a constituent of the fertilization envelope of the sea urchin Strongylocentrotus purpuratus, that has revealing characteristics of how the envelope might form and what protein interaction domains might predominate. We present the largest cDNA sequence we were able to identify representing approximately two thirds of the predicted protein coding region. The C-terminal half of the cognate SFE1 protein contains two different amino acid repeat motifs: a cysteine-rich (15%) motif of 40 amino acids that is tandemly repeated 22 times and is followed by a serine/threonine-rich (38%) repeat of 63 amino acids that is tandemly repeated 3.5 times. Surprisingly, just N-terminal to the cysteine-rich repeat region is a sequence of five repeats with similarity to repeats in another cortical granule protein, SFE9, and to the motif originally identified in the receptor of low-density lipoproteins, the LDLr motif. The amino acid composition deduced from the partial SFE1 cDNA is similar also to the composition of proteoliaisin, a protein thought to tether the ovoperoxidase to the vitelline layer of the egg and thereby sequester the crosslinking activity of the ovoperoxidase to a limited population of proteins in the fertilization envelope. However, by use of monoclonal and polyclonal antibodies to SFE1 and proteoliaisin, we show here that they are distinct gene products. We also show that SFE1 is packed selectively into the cortical granules and then is crosslinked into the fertilization envelope following fertilization. In situ RNA hybridization analysis shows that the mRNA of SFE1 (9 kilobases) is present in oocytes selectively and is turned over rapidly in the oocyte following germinal vesicle breakdown. Our findings suggest that the gene encoding this major product of the egg is activated concomitantly with the other cortical granule-specific products already identified, and that a common LDLr-like motif of the fertilization envelope may reveal a structural mechanism for protein interactions in its construction.

Amino Acid Sequence↗
PubMed1987

The effect of nitrous oxide on in vitro fertilization success rate.

The authors studied the effect of nitrous oxide on success rates for in vitro fertilization and pregnancy in women undergoing laparoscopy for oocyte retrieval. Ninety-eight patients in an in vitro fertilization program were randomly assigned to an anesthetic regimen including either 0.7% (end-tidal) isoflurane with 60% nitrous oxide in oxygen, or 1.4% (end-tidal) isoflurane in oxygen. Success rates for fertilization and pregnancy in 44 additional patients who declined randomization were also studied. Among the 51 randomized patients who did not receive nitrous oxide, 192 oocytes were obtained and 122 fertilized (63.5%), resulting in eight pregnancies (16.3%). From the 47 randomized patients given nitrous oxide, 168 oocytes were retrieved and 114 fertilized (67.9%), resulting in nine pregnancies (19.1%). No significant differences between rates of fertilization or pregnancy emerged between groups. Such differences would have been found with an 80% probability had nitrous oxide had a 20% effect on oocyte fertilization.

Female↗
PubMed1991

Fertility rates in men with normal semen characteristics: spermatozoal testing by induction of the acrosome reaction and Wright-Giemsa staining for subtle abnormal forms.

Little is known about the fertility potential of semen from men who fulfill the accepted criteria of normal semen quality. We examined retrospectively the fertility rates of semen donors with normal semen quality. Donor performance was evaluated in women who had no known infertility factors or had only ovulatory dysfunction corrected by clomiphene. Cycles of therapeutic donor insemination were monitored for ovulation, and pregnancy outcome was followed up. Pregnancy resulted from therapeutic donor insemination with 21 donors and did not result in pregnancy with five (the range of the percentage of cycles in which pregnancy occurred was zero to 31). The comparison of donor semen analysis characteristics with pregnancy rates indicated that the total number of motile spermatozoa per ejaculate correlated with pregnancy rate (P = .04). Cox proportional hazard regression analysis showed that when the value for percentage of abnormal forms was combined with the total number of motile spermatozoa, a significant negative association was found between abnormal forms and conception (P = .04). Experiments comparing semen from high-fertility donors (top quartile of pregnancy rate) and low-fertility donors (lowest quartile) demonstrated a greater proportion of spermatozoa with inducible acrosome reactions in the high-fertility group (P less than .05). A Wright-Giemsa stain used to detect subtle abnormal forms in spermatozoa did not discriminate between the groups. These data suggest that differences in fertility potential exist among donors, even though all may exceed the accepted criteria for normal semen quality. Differences in the ability of spermatozoa to capacitate or undergo the acrosome reaction may be a mechanism for diminished fertility in donors with normal semen characteristics.

Acrosome↗
PubMed2006

Radioactive rock phosphate: the feed stock of phosphate fertilizers used in Pakistan.

The existence of natural radioactivity in phosphate fertilizers originates from the rock phosphate that is used as a feed stock for the manufacturing of various types of phosphate fertilizers. Gamma ray activity mass concentrations have been determined in phosphate rock and fertilizer samples collected from different fertilizer manufacturing factories and suppliers in Pakistan. The technique of gamma ray spectrometry was applied using a HPGe (high purity germanium) gamma ray detector coupled with a personal computer (PC) based multichannel analyzer (MCA). The specific activity values of 40K, 226Ra, and 232Th were widely distributed in the rock and fertilizer samples. Activity mass concentrations of 238U (226Ra) in the rock phosphate from Jordan and Pakistan were 428 +/- 11 and 799 +/- 10 Bq kg(-1), respectively, and that in the triple-superphosphate fertilizer was 701 +/- 21 (-1), which was greater than the average values of 238U (226Ra) for other types of fertilizers under study. The concentrations of 40K and 232Th were of the order of background level on the Earth's crust. Chemical analysis for concentration of different constituents in rock phosphate was also carried out. The higher the concentrations of P2O5 and K2O were, the higher the specific activities of 226Ra and 40K were, respectively, in the rocks under study. The amount of radioactivity in the rock phosphate is a source of continuous exposure to radiation, which varies widely depending upon the origin and grade of rock; therefore, radiation dose rate has been estimated. The values of dose rate and other derived quantities were many folds larger than the limits specified for those quantities.

Fertilizers↗
PubMed1997

Fertility control as a means of controlling bovine tuberculosis in badger (Meles meles) populations in south-west England: predictions from a spatial stochastic simulation model.

A spatial stochastic simulation model was used to assess the potential of fertility control, based on a yet-to-be-developed oral bait-delivered contraceptive directed at females, for the control of bovine tuberculosis in badger populations in south-west England. The contraceptive had a lifelong effect so that females rendered sterile in any particular year remained so for the rest of their lives. The efficacy of fertility control alone repeated annually for varying periods of time was compared with a single culling operation and integrated control involving an initial single cull followed by annually repeated fertility control. With fertility control alone, in no instance was the disease eradicated completely while a viable badger population (mean group size of at least one individual) was still maintained. Near eradication of the disease (less than 1% prevalence) combined with the survival of a minimum viable badger population was only achieved under a very limited set of conditions, either with high efficiency of control (95%) over a short time period (1-3 years) or a low efficiency of control (20%) over an intermediate time period (10-20 years). Under these conditions, it took more than 20 years for the disease to decline to such low levels. A single cull of 80% efficiency succeeded in near eradication of the disease (below 1% prevalence) after a period of 6-8 years, while still maintaining a viable badger population. Integrated strategies reduced disease prevalence more rapidly and to lower levels than culling alone, although the mean badger group size following the onset of control was smaller. Under certain integrated strategies, principally where a high initial cull (80%) was followed by fertility control over a short (1-3 year) time period, the disease could be completely eradicated while a viable badger population was maintained. However, even under the most favourable conditions of integrated control, it took on average more than 12 years following the onset of control for the disease to disappear completely from the badger population. These results show that whilst fertility control would not be a successful strategy for the control of bovine tuberculosis in badgers if used alone, it could be effective if used with culling as part of an integrated strategy. This type of integrated strategy is likely to be more effective in terms of disease eradication than a strategy employing culling alone. However, the high cost of developing a suitable fertility control agent, combined with the welfare and conservation implications, are significant factors which should be taken into account when considering its possible use as a means of controlling bovine tuberculosis in badger populations in the UK.

Animals↗
PubMed2001

The influence of mineral fertilizer combined with a nitrification inhibitor on microbial populations and activities in calcareous Uzbekistanian soil under cotton cultivation.

Application of fertilizers combined with nitrification inhibitors affects soil microbial biomass and activity. The objective of this research was to determine the effects of fertilizer application combined with the nitrification inhibitor potassium oxalate (PO) on soil microbial population and activities in nitrogen-poor soil under cotton cultivation in Uzbekistan. Fertilizer treatments were N as urea, P as ammophos, and K as potassium chloride. The nitrification inhibitor PO was added to urea and ammophos at the rate of 2%. Three treatments--N200 P140 K60 (T1), N200 PO P140 K60 (T2), and N200 P140 PO K60 (T3) mg kg(-1) soil--were applied for this study. The control (C) was without fertilizer and PO. The populations of oligotrophic bacteria, ammonifying bacteria, nitrifying bacteria, denitrifying bacteria, mineral assimilating bacteria, oligonitrophilic bacteria, and bacteria group Azotobacter were determined by the most probable number method. The treatments T2 and T3 increased the number of oligonitrophilic bacteria and utilization mineral forms of nitrogen on the background of reducing number of ammonifying bacteria. T2 and T3 also decreased the number of nitrifying bacteria, denitrifying bacteria, and net nitrification. In conclusion, our experiments showed that PO combined with mineral fertilizer is one of the most promising compounds for inhibiting nitrification rate, which was reflected in the increased availability and efficiency of fertilizer nitrogen to the cotton plants. PO combined with mineral fertilizer has no negative effects on nitrogen-fixing bacteria Azotobacter and oligo-nitrophilic bacteria.

Agriculture↗
PubMed1992

How common are polycystic ovaries in normal women and what is their significance for the fertility of the population?

OBJECTIVE: We wished to determine the prevalence of polycystic ovaries (PCO) and relate morphological appearance to fertility. DESIGN: We sent postal invitations to a random sample of women born in the years 1952-1969 from a list of a single Group Practice to attend for reproductive history questionnaire, examination, ultrasound scan of the ovaries and hormone measurements within 5 days of the onset of menstruation. SUBJECTS: Of 1065 women potentially available for study, 571 (54%) replied of whom 353 (62%) agreed to participate. One hundred and ninety (18%) completed the study, 163 were deferred (57 because of current or very recent pregnancy, 106 because of inconvenience at time approached), and 18 additional women volunteered. MEASUREMENTS: Prevalence of polycystic ovaries, ovarian size and morphology, menstrual history, features of androgen excess, fertility status, serum hormone levels. RESULTS: The prevalence of PCO was 22% (41/190). PCO and non-PCO women were similar with respect to age, body mass index, oral contraceptive pill (OCP) usage, acne, and menstrual pattern but hirsutism (Ferriman and Gallwey score > 7) was significantly (P = 0.006) more frequent among PCO women. Proven prior fertility was the same in PCO (56%) and non-PCO (64%) women and an equal proportion in each group had not yet tested their fertility. Of those women with previously proven fertility, self-perceived difficulty in conception occurred in similar proportions of women with and without PCO. Unresolved primary or secondary infertility (2.5-4%) was similar in both groups. Ovarian volume (each ovary separately) was larger in women with PCO irrespective of current OCP usage. Serum levels of oestradiol and FSH were similar in PCO and non-PCO women, but LH was distributed around a higher median in PCO women. Median testosterone and androstenedione levels were the same in PCO and non-PCO women. CONCLUSIONS: The prevalence of polycystic ovarian morphology is high but, in this sample of women, was accompanied by minimal clinical manifestations and apparently no deleterious effects on earlier fertility. An isolated finding of polycystic ovaries may be a normal variation and should not necessarily imply altered fertility potential.

Adult↗
PubMed1989

Fertilization of human oocytes in vitro by spermatozoa from oligozoospermic and normospermic men.

Sperm were isolated from the semen of oligozoospermic (less than 20 x 10(6) sperm/ml) and normospermic (greater than or equal to 20 x 10(6) sperm/ml) men in an in-vitro fertilization (IVF) programme. Oocytes from the female partners were inseminated with either 75 or 100 x 10(3) motile sperm and checked for fertilization after 16-20 h. A significant reduction in the overall fertilization rate of oocytes was seen for the oligozoospermic group compared to the normospermic group, at both insemination concentrations. In the oligozoospermic group, a fertilization rate of 31% (19/61) was achieved when oocytes were inseminated with 75 x 10(3) sperm, and 38% (9/24) when inseminated with 100 x 10(3) sperm. This compared with rates of 57% (397/696) and 64% (650/1018), respectively, for normospermic cases at both insemination concentrations. No evidence of fertilization was seen in 36% (4/11) and 67% (4/6) of oligozoospermic cases when 75 or 100 x 10(3) sperm were used, compared with values of 13% (17/133) and 9% (20/212), respectively, in normospermic cases. After excluding zero cases, the fertilization rate of oocytes for the oligozoospermic group (75%; 9/12) was similar to the normospermic group (70% 650/935) when 100 x 10(3) sperm were used. However, when 75 x 10(3) sperm were used, the fertilization rate for the oligozoospermic group (41%; 19/46) was significantly lower than that of the normospermic group (62%; 397/645). Following the transfer of embryos into the female partner, clinical pregnancies were diagnosed in 2/7 (29%) oligozoospermic cases and 27/267 (10%) normospermic cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1992

The role of the seminal vesicles and coagulating glands in fertilization in the rat.

To investigate the role of the seminal vesicles (SV) and coagulating glands (CG) in fertilization in the rat, partial resections of the SV (25%--group B), 50%--group C, and 75%--group D) or bilateral resection of the SV alone (100%--group E), or together with the CG (group F) were undertaken. In other groups, bilateral resection of the CG only (group G), or bilateral resection of the CG with ipsilateral SV resection (group H) were performed. A group of sham-operated rats served as controls (group A). There were no significant differences among groups A, B, C and D in the number of fertile rats post-operatively but significant differences were evident in groups E, F, G, H when compared with the control group (P less than 0.01 for all groups). Only the fertile rats were able to form copulatory plugs (CP) post-operatively. Bilateral ligation of the SV ducts was performed in ten fertile rats. Post-operatively, the proportion of fertile rats was decreased significantly (P less than 0.01). Removal of the ligatures resulted in a significant increase (P less than 0.01) in fertility. It was also demonstrated that the addition of rat seminal vesicular secretions (SVS) to epididymal sperm suspensions resulted in a significant decrease (P less than 0.001) in sperm motility. These results suggest that the SV and CG are necessary for fertility in rats, and that one role of SVS is the formation of a CP and not the maintenance of sperm motility.

Animals↗
PubMed2006

Bio-social determinants of fertility.

This paper reviews several studies that investigated the potential role of genetic factors in determining fertility outcomes. Our review demonstrates convincingly that fertility contains genetic variance; that is, differences between humans in their genetic make-up affects their fertility outcomes and fertility-related behaviours. This finding is robust using both heritabilities and coefficients of genetic variation, and using both direct measures of fertility outcomes and also fertility precursors like fecundity, marriage, fertility expectations and attempts to get pregnant (proception). Moreover, genetic variance can change over short periods of time or across educational levels, specifically for females, and the relevance of genetic variance seems to increase during times of increasing reproductive choice.

Demography↗
PubMed2006

Fertility rates and future population trends: will Europe's birth rate recover or continue to decline?

Europe has long completed its demographic transition from high birth and death rates to low birth and death rates. But the demographic transition paradigm that has been very useful for explaining global demographic trends during the 20th century and that still has strong predictive power when it comes to projecting future trends in countries that still have high fertility, has nothing to say about the future of fertility in Europe. The currently popular notion of a 'second demographic transition' is a useful way to describe a bundle of behavioural and normative changes that recently happened in Europe, but it has no predictive power. The social sciences have not yet come up with a useful theory to predict the future fertility level of post-demographic transition societies. We even do not know whether the trend will be up or down. Given the lack of a predictive theory, this paper will try to do two things: (i) Summarize different substantive arguments that would either suggest the assumption of a recovery of fertility rates in Europe or alternatively, imply further declines. (ii) Convert this discussion of the uncertainty of future fertility trends into probabilistic population projections for Europe, thus highlighting the implications of alternative fertility levels over the coming years. We will also discuss trade-offs between fertility and immigration, and the phenomenon that Europe now has entered a period of negative momentum of population growth.

Birth Rate↗