I have read on a few occasions that sex during the infertile period isn't necessarily a good idea (for want of a better word) for example:
Embryonic health[edit source | editbeta]
It has been suggested that unprotected intercourse in the infertile periods of the menstrual cycle may still result in conceptions, but create embryos incapable of implanting. It has also been suggested that pregnancies resulting from method failures of periodic abstinence methods are at increased risk of miscarriage and birth defects due to aged gametes at the time of conception. Other research suggests that timing of conception has no effect on miscarriage rates, low birth weight, or preterm delivery.
And this study which suggests that having had a miscarriage in the past, delaying conception increases increases the risk of another one. ncbi.nlm.nih.gov/pubmed/7755073
I just wondered what people-interested-in-biology's thoughts on this were...