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Excerpt
Wohlfahrt et al1 evaluated the effect of short and long interpregnancy intervals for preventing the risk of spontaneous abortion. They observed a U-shaped distribution with higher risks when the interval was less than 6 months or more than 5 years, which is consistent with the findings for low birth weight, preterm birth, and intrauterine growth retardation. 2 The effect of very short interpregnancy intervals in these various segments of the continuum of reproductive wastage is also evident in adulthood, particularly for female reproductive function (for example, menstrual disorders, proneness to recurrent miscarriage, childlessness, and stillbirth). 3
In the earlier study, 2 no distinction could be made between situations in which the preceding pregnancies ended either in a livebirth or in a spontaneous abortion. Therefore, Wohlfahrt et al1 analyzed these categories separately. In women who became pregnant less than 6 months after a livebirth, the adjusted relative risk was 1.10 (95% confidence interval = 0.99–1.22), whereas after a spontaneous abortion the risk was 0.95 (95% confidence interval = 0.85–1.05). Wohlfahrt et al1 worried about the interpretation of the lowest risk after the shortest time interval, particularly because many couples might try to conceive again shortly after. We suggest that the lowest risk directly after a spontaneous abortion is the result of a “dose-response fallacy,” as presented by Selevan and Lemasters, 4 or a “distortion by differential loss,” by Khoury et al.5 Anovulatory subfecundity and restoration of the ovulatory pattern in very short interpregnancy intervals are characterized by prolonged preovulatory phases. 6 Nonoptimal molecular, biochemical, and physiological maturation of the oocyte, that is, overripeness ovopathy, refers to experimentally induced aging of the oocyte before or after ovulation. 6 Teratologic effects of overripeness ovopathy result in misimplantation and are “dose” dependent: the higher its degree, the smaller the probability of implantation and hence, the smaller the risk of ongoing pregnancy or increased risk of ending in a lost pregnancy. Accumulation of pathologic conceptions directly after a spontaneous abortion and inherent loss of pregnancy, therefore, may cause a dose-response fallacy and explain the apparent reduced risk of wastage.
Restoration of the ovulatory pattern and inherent overripeness ovopathy also explain the higher risks of spontaneous abortions for long (unintended) pregnancy intervals and account for the U-shaped curve with higher risks among the very young (<15 years) and advanced (>35 years) maternal age. 2,7 The menstrual cycles and ovulatory rates in these (and other) conditions are highly disturbed and characterized by a tendency toward disproportionate attrition and pregnancy loss.
