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Letters to the editor: Author’s reply
| Content Provider | Semantic Scholar |
|---|---|
| Author | Mead, Donald J. |
| Copyright Year | 1995 |
| Abstract | Sex ratio at birth and latitude EDITOR,—Grech et al 1 report that sex ratio (proportion male) at birth declines highly significantly with increase in geographical latitude in Europe. They wonder if this is an eVect of temperature variation. This may be so, but I suggest that variations in maternal hormone levels are a proximate cause. The reason for suggesting this is as follows. I have reported highly significant correlations between latitude and (a) birth weight and (b) maternal age standardised dizygotic (DZ) twinning rates across the countries of Europe and the states of the United States. Birth weight and DZ twinning rates are both higher at more extreme latitudes. 2 There is direct 3 and indirect 4 evidence that maternal oestrogen levels correlate with the birth weights of their infants. Moreover maternal oestrogen levels reportedly correlate with the probability of bearing a pair of DZ twins. 5 Lastly, there is good evidence that maternal hormone (including oestrogen) levels at the time of conception partially control the sexes of oVspring. 6 Bearing in mind Occam's Razor, it is tempting to propose that one cause (variation in maternal hormone levels) is at least partially responsible for all three eVects—including the variation of sex ratio with latitude. Declining male births with increasing geographical latitude in Europe. et al. Maternal determinants of birth weight : a population based sample from Qingdao, China. 5 Martin NG, de Kretser DM, Robertson DM, et al. Elevation of follicular phase inhibin and LH levels in mothers of dizygotic twins suggests nonovarian control of human multiple ovula-tion. Fertil Steril 1991;56:469–74. 6 James WH. Evidence that mammalian sex ratios at birth are partially controlled by parental hormone levels at the time of conception. EDITOR,—Dr James may well be correct in that maternal oestrogen levels during pregnancy may play a part in determining the sex of oVspring. Such external influences could be multiple, and include not only temperature variations and maternal hormone levels, but also other, as yet unsuspected factors. An interesting study would be the analysis of seasonal variations of sex ratios at birth, for individual countries. A latitude eVect would thus be excluded, and any variations in the birth sex ratio would be more likely to be caused by a temperature variation eVect. CORRECTIONS An authors' error occurred in the paper by Evans and others (2000;54:677–86). Because of a computing error, missing data were not excluded from some of … |
| Starting Page | 695 |
| Ending Page | 695 |
| Page Count | 1 |
| File Format | PDF HTM / HTML |
| DOI | 10.1006/jsvi.1995.0481 |
| Alternate Webpage(s) | http://jech.bmj.com/content/jech/55/3/216.1.full.pdf |
| Alternate Webpage(s) | https://doi.org/10.1006/jsvi.1995.0481 |
| Volume Number | 186 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Letter |
