Editing Calendar-based contraceptive methods (section)

===Embryonic health===
It has been suggested that pregnancies resulting from failures of periodic abstinence methods are at increased risk of miscarriage and birth defects due to aged gametes at the time of conception.<ref>{{cite journal | author=Gray, RH | title=Aged gametes, adverse pregnancy outcomes and natural family planning. An epidemiologic review |journal=Contraception |date=October 1984 |volume=30 |issue=4 |pages=297–309 |pmid=6509983 |doi=10.1016/S0010-7824(84)80022-0 }}</ref> Other research suggests that timing of conception has no effect on miscarriage rates,<ref>{{cite journal |vauthors=Gray RH, Simpson JL, Kambic RT | title=Timing of conception and the risk of spontaneous abortion among pregnancies occurring during the use of natural family planning | journal=American Journal of Obstetrics and Gynecology |date=May 1995 | volume=172 | issue=5 | pages=1567–1572 | pmid=7755073 | doi=10.1016/0002-9378(95)90498-0 }}</ref> low birth weight, or preterm delivery.<ref>{{cite journal |vauthors=Barbato M, Bitto A, Gray RH |title=Effects of timing of conception on birth weight and preterm delivery of natural family planning users |journal=Advances in Contraception |date=June–September 1997 |volume=13 |issue=2–3 |pages=215–228 |pmid=9288339 |doi=10.1023/A:1006508106197 |s2cid=24939823 |display-authors=etal}}</ref>