A great number of case reports on concordant and discordant twins with oculo-auriculo-vertebral spectrum (OAVS) suggest that there might be an association between reproductive abnormalities, twinning and OAVS. The etiology of OAVS is unknown, but may involve epigenetic dysregulation of the oocyte or early embryo. We collected data on fertility and pregnancy outcome of 72 parents of patients with sporadic OAVS. We also evaluated prospective follow-up data on 3.372 fetuses and children conceived by intracytoplasmatic sperm injection (ICSI). Parental age, duration of menstrual cycle and the incidence of spontaneous abortion was not different when compared to the German population. However, there is an excess of parents who have used assisted reproductive techniques (ART; retrospective P = 0.038, prospective P = 0.023) and an excess of twins among naturally conceived patients with OAVS (P = 0.0025). An excess of ART conceptions and monozygotic twinning in OAVS is compatible with the concept of overripeness ovopathy as proposed by Jongbloet (Maandschr Kindergeneeskd 36:352-367, 1968).

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Current hypotheses do not explain the concerns about sex ratio modulation at conception, birth or during life, and particularly about sex ratio reversal, e.g. at very young or advanced maternal age, during 'anovulatory seasons', among those of low socio-economic status, or induced by specific lifestyles, etc. These modulations are explained by the introduction of the ovopathy concept and inherent preferential fertilization of non-optimally matured oocytes by Y-bearing sperm. Non-optimal development and implantation of male-biased fetuses results in perennial loss of non-optimal, male-biased fetuses before and after birth. Accumulation of conceptopathology in extreme conditions entrains an increasing male to female ratio and ultimately a decreasing one, i.e. an 'inverted dose-response gradient' or 'dose-response fallacy'.

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The relationship between fecundability and month of birth was investigated in a cohort of 1526 women who married between 1802 and 1929, using only women whose first marriage occurred before the age of 35 years. On the basis of their time to pregnancy (TTP, calculated as time between wedding and first birth minus gestational length), women were categorized into two groups: fecunds (TTP up to 12 months or prenuptial conceptions, n = 1348) and subfecunds (TTP >18 months, n = 118). By use of logistic regression, cosinor functions with a period of 1 year or 6 months and variable shift and amplitude were fitted through the monthly odds of subfecunds versus fecunds. The best fitting curve was unimodal, with a zenith in September (P = 0.13 for H0: no differences). Exclusion of childless women (n = 36, minimum follow-up 5 years) from the subfecunds led to a similar curve (P < 0.01), while childless women, as compared with fecunds, showed a birth distribution that was best represented with a bimodal curve with zeniths in January and July (P = 0.06). This study provides evidence for the existence of differences in fecundability by month of birth. The cause of this relationship is unclear, but may lie in a melatonin-dependent circannual variability of the quality of the oocyte.