Sex Ratio Associated with Natural Family Planning

Pérez, A.; Eger, R.; Domenichini, V.; Kambic, Robert T.; Gray, Ronald H.

doi:10.1016/s0015-0282(16)48337-8

Cited by 21 publications

(9 citation statements)

References 7 publications

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“…The idea that mucus filtration selects for Y spermatozoa either by allowing more, smaller Y spermatozoa to reach the fallopian tubes, or allows them to reach the tubes in better condition, is consistent with reports that the SRb declines with decreasing mucus viscosity and sperm selection as the time of the responsible insemination approaches ovulation day (Guerrero, 1974;WHO, 1980;Perez, et al, 1982;France, et al, 1984). It may also be consistent with reports in which there are multiple inseminations in the fertile period and the SRb does not decline as the time of the estimated (usually the last) responsible insemination approaches the time of ovulation ( Spira, et al, 1993;Weinberg, et al, 1995).…”

Section: Introductionsupporting

confidence: 78%

Female genital cutting and mother's age at birth are associated with the sex of offspring in Africa

Martina¹,

Williams

2008

Biodemography and Social Biology

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Female genital cutting (FGC) is widespread in Africa. Its short and long term medical consequences are widely reported. Here we report that FGC is associated with and may contribute to increases in the sex ratio at birth (Odds Ratio = 1.019; 95% C.I. = 1.007, 1.032) while mother's age at birth is inversely associated with probability of male birth (Odds Ratio = 0.998; 95% C.I. = 0.997, 0.999) in a generalized linear, logistic model with the probability of a male birth the dependent variable and eight potential explanatory variables applied to 413,384 births in 22 African countries. While these two associations are statistically significant, their odds ratios are close to 1.0 and they only slightly decrease the null deviance of the model. Therefore sex determination in these data is still a mostly stochastic process determined by the random variation in X or Y sperm production, transport, and conception.

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Section: Introductionsupporting

confidence: 78%

Female genital cutting and mother's age at birth are associated with the sex of offspring in Africa

Martina¹,

Williams

2008

Biodemography and Social Biology

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“…Our results support the hypothesis that a long interval between coitus and ovulation could correlate with a higher sex ratio at birth. The sex ratio has been reported to be between 0.58 and 0.61 when intercourse was timed before and after the most fertile period (Perez et al ., 1985; France et al ., 1992). It has been reported to increase to 0.683 when intercourse preceded the basal body temperature rise by 6 or more days, which was approximately 5 or more days prior to ovulation/fertilization (Guerrero, 1974).…”

Section: Discussionmentioning

confidence: 99%

Differential binding of X- and Y-chromosome-bearing human spermatozoa to zona pellucidain vitro

2001

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The sex of human offspring has been associated with the day in the mother's menstrual cycle on which insemination occurs, with male zygotes being formed earlier in the fertile period than female zygotes. Using an in vitro environment designed to mimic the in vivo milieu, we tested the hypothesis that Y-chromosome-bearing spermatozoa survive functionally longer than X-chromosome-bearing spermatozoa, and that this differential functional survival is a contributing factor to the in vivo phenomenon. Donor semen was processed by swim-up and incubated at 37 degrees C in culture medium for 0, 24 and 48 h, with human zona pellucida (hemizona, HZ) being used to select functional spermatozoa. A second set of in vitro storage conditions, 4 degrees C in test-yolk refrigeration buffer, was used to determine whether changing the incubation conditions alters the process. The sex chromosome of the spermatozoa was determined using fluorescent in situ hybridization (FISH). For spermatozoa incubated at 37 degrees C, the percentage of functional (HZ bound) Y-bearing spermatozoa was significantly increased (P < 0.05) at 48 h (55.4 + 2.9%) but not at 0 h (50.5 + 0.7%) or 24 h (52.8 + 3.1%) compared to swim-up spermatozoa (50.6 + 0.3%). No difference in the percentage of functional Y-spermatozoa was observed at any time-point with storage at 4 degrees C in refrigeration buffer. Thus, we demonstrated that significantly more Y-bearing spermatozoa were capable of zona binding than X-bearing spermatozoa at 48 h at 37 degrees C incubation, with an observed Y : X ratio of 1.15 for these zona-bound spermatozoa compared to 1.02 for post-swim-up spermatozoa. We conclude that a differential functional survival appears to exist between X-bearing and Y-bearing spermatozoa, with the latter exhibiting a longer functional survival under in vitro conditions.

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“…There have been mixed results from studies that have attempted to determine whether the timing of insemination affects offspring sex, with some reporting an effect (e.g. Harlap 1979;Perez et al 1985;James 2000) and others not (e.g. Wilcox et al 1995;Gray et al 1998).…”

Section: Introductionmentioning

confidence: 99%

Trends in Population Sex Ratios May be Explained by Changes in the Frequencies of Polymorphic Alleles of a Sex Ratio Gene

Gellatly

2008

Evol Biol

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A test for heritability of the sex ratio in human genealogical data is reported here, with the finding that there is significant heritability of the parental sex ratio by male, but not female offspring. A population genetic model was used to examine the hypothesis that this is the result of an autosomal gene with polymorphic alleles, which affects the sex ratio of offspring through the male reproductive system. The model simulations show that an equilibrium sex ratio may be maintained by frequency dependent selection acting on the heritable variation provided by the gene. It is also shown that increased mortality of prereproductive males causes an increase in male births in following generations, which explains why increases in the sex ratio have been seen after wars, also why higher infant and juvenile mortality of males may be the cause of the male-bias typically seen in the human primary sex ratio. It is concluded that various trends seen in population sex ratios are the result of changes in the relative frequencies of the polymorphic alleles of the proposed gene. It is argued that this occurs by common inheritance and that parental resource expenditure per sex of offspring is not a factor in the heritability of sex ratio variation.

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Sex Ratio Associated with Natural Family Planning

Cited by 21 publications

References 7 publications

Female genital cutting and mother's age at birth are associated with the sex of offspring in Africa

Female genital cutting and mother's age at birth are associated with the sex of offspring in Africa

Differential binding of X- and Y-chromosome-bearing human spermatozoa to zona pellucidain vitro

Trends in Population Sex Ratios May be Explained by Changes in the Frequencies of Polymorphic Alleles of a Sex Ratio Gene

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