University of Szeged, Department of Obstetrics and Gynaecology, Semmelweis u. 1. H-6725, Szeged, Hungary
Dear Sir,
We read with interest the article (Jacobsen et al., 1999) analysing the effects of multiple birth, birth order, age of parents and the sexes of preceding siblings on the secondary sex ratio. The maternal age, maternal parity and sexes of the previous children in the family were found to have no significant effect on the sex ratio.
The literature from 1950 to the present indicated a declining trend in the male ratio (Moller, 1996; Van der Pal-de Bruin et al., 1997
). In Hungary too a pronounced decrease was observed between 1950 and 1990. However, from 1991 to 1999 there was a gradual increase, except in 1998 (Figure 1
).
|
|
|
References
Moller, H. (1996) Change in male:female ratio among newborn infants in Denmark. Lancet, 348, 828829.[Medline]
Van der Pal-de Bruin, K.M., Verloove-Vanhorick, S.P. and Roeleveld, N. (1997) Change in male:female ratio among newborn babies in Netherlands. Lancet, 349, 62.[Medline]
Jacobsen, R., Moller, H. and Mouritsen, A. (1999) Natural variation in human sex ratio. Hum. Reprod., 14, 31203125.