Aged gametes, adverse pregnancy outcomes and natural family planning. An epidemiologic review.

Unconfirmed epidemiologic studies suggest a possible increased risk of birth defects associated with Natural Family Planning (NFP) use, and an increased incidence of spontaneous abortion or frequency of chromosomal abnormalities in abortuses associated with conceptions outside the most "fertile period". The risk is approximately two- to four-fold, but the evidence is by no means conclusive. The implication for NFP depends on the frequency of method failures in user populations, but is not likely to constitute a major hazard. Further research could utilize a data bank of NFP charts.