Sex ratios in fetuses and liveborn infants with autosomal aneuploidy

Abstract

Ten data sources were used substantially to increase the available data for estimating fetal and livebirth sex ratios for Patau (trisomy 13), Edwards (trisomy 18), and Down (trisomy 21) syndromes and controls. The fetal sex ratio estimate was 0.88 (N = 584) for trisomy 13, 0.90 (N = 1702) for trisomy 18, and 1.16 (N = 3154) for trisomy 21. All were significantly different from prenatal controls (1.07). The estimated ratios in prenatal controls were 1.28 (N = 1409) for CVSs and 1.06 (N = 49427) for amniocenteses, indicating a clear differential selection against males, mostly during the first half of fetal development. By contrast, there were no sex ratio differences for any of the trisomies when comparing gestational ages <16 and >16 weeks. The livebirth sex ratio estimate was 0.90 (N = 293) for trisomy 13, 0.63 (N = 497) for trisomy 18, and 1.15 (N = 6424) for trisomy 21, the latter two being statistically different than controls (1.05) (N = 3660707). These ratios for trisomies 13 and 18 were also statistically different than the ratio for trisomy 21. Only in trisomy 18 did the sex ratios in fetuses and livebirths differ, indicating a prenatal selection against males >16 weeks. No effects of maternal age or race were found on these estimates for any of the fetal or livebirth trisomies. Sex ratios for translocations and mosaics were also estimated for these aneuploids. Compared to previous estimates, these results are less extreme, most likely because of larger sample sizes and less sample bias. They support the hypothesis that these trisomy sex ratios are skewed at conception, or become so during embryonic development through differential intrauterine selection. The estimate for Down syndrome livebirths is also consistent with the hypothesis that its higher sex ratio is associated with paternal nondisjunction. © 1996 Wiley‐Liss, Inc.

Gender Affects Clinical Suspicion of Down Syndrome

“…Several hypotheses have been put forward to explain the skewed sex ratio in Down syndrome. Meiotic disturbance (non-homologous co-orientation in male meiosis) [Kovaleva, 1992;Petersen et al 1993], fertilization event (greater accessibility of Y-bearing sperm to ova disomic for chromosome 21 or promotion of non-disjunction in the ova by Y-bearing sperm) [Ferguson-Smith & Yates, 1984;Kovaleva & Mutton, 2005], and post-fertilization events (intrauterine selection against females) [Huether et al, 1996;Hook et al, 1999] have been discussed. Data from recent studies supports suggestion that male excess among live born with non mosaic trisomy 21 might be due to selection against female fetuses [Oliver et al, 2009;Kovaleva, 2010].…”

Trisomy 18: Changes in sex ratio during intrauterine life

“…The present study confirms the observation by Hook et al [1989] and the results from Huether et al [1996] and presents more details in risk calculation for the different sexes in prenatal diagnosis of trisomy 18. We conclude on the basis of this study that in trisomy 18 after 18 weeks of gestation, the risk for intrauterine demise in males is twice as high as the risk for intrauterine demise in females.…”

Survival with trisomy 18—data from Switzerland

“…Therefore, most of the affected fetuses die during pregnancy [Hook et al, 1983;Gardner and Sutherland, 1996] and only a very small proportion come to term. There are distinctly more females than males born, whereas in prenatally diagnosed cases, the sex ratio is about 0.9 (male:female) [Huether et al, 1996]. Children with trisomy 18 show multiple malformations, a specific pattern of dysmorphic signs and profound mental deficiency.…”