Where Have All the Conceptions Gone?

Roberts, Colin; Lowe, Charles U.

doi:10.1016/s0140-6736(75)92837-8

Cited by 245 publications

(99 citation statements)

References 9 publications

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“…Overall loss may be much higher in many cases, for example, Brambell (1948) esti- mated the minimum total wastage of ova produced by wild rabbits to be 43.3%, of which between 10.2 and 13.0% are lost before implantation and most of the remainder before mid-term. In humans, an estimated minimum 30% of all fertilized ova are lost during early pregnancy (Roberts & Lowe 1975). Known causes of reproductive loss include chromosomal anomalies, endocrine disorders and physiological abnormalities, although ca.…”

Section: Discussionmentioning

confidence: 99%

Female multiple mating behaviour, early reproductive failure and litter size variation in mammals

Stockley

2003

Proc. R. Soc. Lond. B

105

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Female promiscuity is widespread among mammals, although its function is poorly understood. Recently, much interest has been generated by the hypothesis that female promiscuity, combined with postcopulatory paternity-biasing mechanisms, may function to reduce the costs of reproductive failure resulting from genetic incompatibility. Here, a comparative approach is used to determine if average rates of reproductive failure differ for polytocous mammal species with contrasting levels of female multiple-mating behaviour. After control for phylogeny, promiscuous species were found to have significantly lower rates of early reproductive failure than monogamous and polygynous species, in which females are relatively monandrous. Monandrous females appear to compensate for higher early reproductive failure with increased ova production, and thus produce comparable average litter sizes to those of more promiscuous females. However, there is significantly more variation around the average litter sizes produced by relatively monandrous females. These findings are broadly consistent with predictions of the genetic incompatibility avoidance hypothesis, although it is emphasized that alternative explanations cannot be ruled out on the basis of the comparative evidence presented. Further studies are needed to explore ecological correlates of multiple-mating behaviour, to investigate potential post-copulatory paternity-biasing mechanisms, and to identify the causes of reproductive failure in natural mammal populations.

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Section: Discussionmentioning

confidence: 99%

Female multiple mating behaviour, early reproductive failure and litter size variation in mammals

Stockley

2003

Proc. R. Soc. Lond. B

105

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“…The unknown mechanisms may be selective fertilization, selective implantation, or losses during embryonic development and foetal growth. 48 The high primary sex ratio at fertilization (160 males to 100 females) that gets closer to unity towards birth [49][50][51][52] and the fact that up to 80% of conceptions are lost [53][54][55] imply a disproportionately high loss of males in utero. One study even located the male-specific prenatal deaths to the embryonic organogenesis period.…”

Section: Discussionmentioning

confidence: 99%

Increased heterozygosity for MHC class II lineages in newborn males

et al. 2002

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“…What happens in week 1?” presented by The Science Museum; available at http://www.sciencemuseum.org.uk/WhoAmI/FindOutMore/Yourbody/Wheredidyoucomefrom/Howdoyougrowinthewomb/Whathappensinweek1: accessed on 22 nd October, 2016), news reports (“Scientists get ‘gene-editing’ go-ahead” by James Gallagher: article at http://www.bbc.co.uk/news/health-35459054: accessed on 22 nd October, 2016), as well as academic philosophical articles 1 and legal judgements 2 . Among reputable scientific publications, including medical and reproductive biology text books, scientific reviews and primary research articles, reported mortality estimates include: 30–70% before and during implantation 3 ; >50% 4 , 73% 5 and 80% 6 before the 6 th week; 75% before the 8 th week 7 ; 70% in the first trimester 8 ; 40–50% in the first 20 weeks 9 ; and 49% 10 , >50% 11, 12 , 53% 13 , 54% 14 , 60% 15 , >60% 16 , 63% 17, 18 , 70% 19– 23 , 50–75% 24 , 76% 5, 25 , 78% 26 , 80–85% 27 , >85% 28 , and 90% 29 total loss from fertilisation to term. The variance in these estimates is striking.…”

Section: Introductionmentioning

confidence: 99%

Early embryo mortality in natural human reproduction: What the data say

Jarvis

2016

F1000Res

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It is generally accepted that natural human embryo mortality during pregnancy is high – losses of 70% and higher from fertilisation to birth are frequently claimed. The first external sign of pregnancy occurs two weeks after fertilisation with a missed menstrual period. Establishing the fate of embryos before this is challenging, and hampered by a lack of data on the efficiency of fertilisation under natural conditions. Four distinct sources are cited to justify quantitative claims regarding embryo loss: (i) a hypothesis published by Roberts & Lowe in The Lancet is widely cited but has no quantitative value; (ii) life table analyses give consistent assessments of clinical pregnancy loss, but cannot illuminate losses at earlier stages of development; (iii) studies that measure human chorionic gonadotrophin (hCG) reveal losses in the second week of development and beyond, but not before; and (iv) the classic studies of Hertig and Rock offer the only direct insight into the fate of human embryos from fertilisation under natural conditions. Re-examination of Hertig’s data demonstrates that his estimates for fertilisation rate and early embryo loss are highly imprecise and casts doubt on the validity of his numerical analysis. A recent re-analysis of hCG study data suggests that approximately 40-60% of embryos may be lost between fertilisation and birth, although this will vary substantially between individual women. In conclusion, it is clear that some published estimates of natural embryo mortality are exaggerated. Although available data do not provide a precise estimate, natural human embryo mortality is lower than is often claimed.

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Where Have All the Conceptions Gone?

Cited by 245 publications

References 9 publications

Female multiple mating behaviour, early reproductive failure and litter size variation in mammals

Female multiple mating behaviour, early reproductive failure and litter size variation in mammals

Increased heterozygosity for MHC class II lineages in newborn males

Early embryo mortality in natural human reproduction: What the data say

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