The effects of genetic and seasonal factors on reproductive success.

Objective: To search for possible effects of two polymorphisms and of the solar cycle of illumination on reproductive success.
Design: Study of haptoglobin (Hp) and ACP1 polymorphisms in consecutive puerperae and analysis of phenotype distribution in relation to time of conception.
Setting: The Maternity Department of Penne Hospital, Penne, Italy.
Patient(s): Three hundred sixty-eight consecutive healthy pueperae from the Caucasian population.
Result(s): The distribution of Hp and ACP1 phenotypes depends on the phase of the solar cycle at conception. Women homozygous for Hp with low ACP1 activity are more likely to conceive in the first part of the year. Women heterozygous for Hp with medium-high ACP1 activity are more likely to conceive in the last part of the year.
Conclusion(s): In the first months of the year there is a steady increase in solar illumination, and this phase corresponds to the best period for reproduction in most plants and animals. This period is also the coldest in the Italian latitudes. Although humans are not seasonal breeders, it is possible that women having a genetic background best adapted to the metabolic demand of the cold period of the year will respond better to reproductive stimuli, resulting in a higher probability of conceiving in the first part of the year.