Human Reproduction, Vol. 16, No. 1, 198,
January 2001
© 2001 European Society of Human Reproduction and Embryology
Letters to the Editor |
Side of ovulation, hormones and sex ratios
The Galton Laboratory, University College London, Wolfson House, 4 Stephenson Way, London NW1 2HE
Dear Sir,
Fukuda et al. (2000) confirm the report of Schöner (1927) that more births follow right-sided ovulation than left-sided ovulation. Fukuda et al. (2000) also report that serum oestradiol and testosterone concentrations are higher in right-sided ovulation than left-sided ovulation. This prompts two suggestions and a prediction.
Suggestion 1
Since women who have ovarian cancer reportedly have higher oestrogen concentrations than controls (Cramer et al., 1994
), the observation of Fukuda et al. (2000) provides an explanation for the finding that ovarian cancers are more common on the right than the left (e.g. Mueller et al., 1950).
Suggestion 2
Clark and Galef (1990) reported that in the Mongolian gerbil, more male offspring than females are gestated in the right uterine horn; and more females than males in the left horn. Clark et al. (1991) further found that this phenomenon holds when the offspring are delivered by Caesarean. Lastly Clark et al. (1994) found (by surgically removing portions of right and left ovaries, and replacing them in right and left ovarian capsules) that `the data are consistent with the hypothesis that lateral asymmetries in gerbil ovaries rather than in gerbil uterine horns cause segregation of gerbil fetuses by sex'. These authors did not identify the nature of these lateral asymmetries. In conformity with my hypothesis (James, 1996), I suggest that they are hormonal: I propose that the gerbil dam, like the human being, has higher oestradiol and/or testosterone levels associated with its right ovary, and that these are responsible for the excess male pups gestated in the right horn.
Prediction
I wish to predict that in natural human pregnancies, boys are more likely to follow right-sided ovulation than left-sided ovulation. This idea was first offered by Hippocrates, and confirmed by Schöner (1927) and derided by Cohen and Stewart (1998). It should be possible to test the idea with the data of Fukuda et al. (2000).
Acknowledgments
I am grateful to Professor U.Mittwoch for references to the laterality of ovarian cancers.
References
Clark, M.M. and Galef, B.G. (1990) Sexual segregation in the left and right horns of the gerbil uterus: `The male embryo is usually on the right, the female on the left' (Hippocrates) Dev. Psychobiology, 23, 29–37
Clark, M.M., Galef, B.G. and Vom Saal, F.S. (1991) Nonrandom sex composition of gerbil, mouse and hamster litters before and after birth. Dev. Psychobiology, 24, 81–90
Clark, M.M., Ham, M. and Galef, B.G. (1994) Differences in the sex ratios of offspring originating in the right and left ovaries of Mongolian gerbils (Meriones unguiculatus). J. Reprod. Fertil., 101, 393–396
Cohen, J. and Stewart, I. (1998) That's amazing, isn't it? New Scientist 17th January, pp 24–28
Cramer, D.W., Barbieri, R.L., Muto, M.G., Kelly, A., Brucks, J.P. and Harlow, B.L. (1994) Characteristics of women with a family history of ovarian cancer: II. Follicular phase hormone levels. Cancer, 74, 1318–1322[Medline]
Fukuda, M., Fukuda, K., Andersen, C.Y. and Byskov, A.G. (2000) Right-sided ovulation favours pregnancy more than left-sided ovulation. Hum. Reprod., 15, 1921–1926
James, W.H. (1996) Evidence that mammalian sex ratios at birth are partially controlled by parental hormone levels at the time of conception. J. Theor. Biol., 180, 271–286[Web of Science][Medline]
Mueller, C.W., Topkins, P. and Lapp, W.A. (1950) Dysgerminoma of the ovary. Am. J. Obstet. Gynecol., 60, 153–159[Medline]
Schöner (1927) Besteht eine Beziehung zwischen dem Geschlechte und der Seite des Corpus-luteum-Sitzes? Schweiz. Med. Woch., Basel. 8, 953–954
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