Making love is the normal expression of love and in nature, sex is absolutely intrinsic to conception and the maintenance of species.
So given this widespread knowledge, you might be very surprised to know that many infertile couples have very little sex.
This, however, doesn't seem to interest many IVF clinics - I'm not sure whether many fertility practitioners ever ask their couples about the frequency of sex before they start on expensive treatments.
In their responses to my questionnaires over 13 years, more than 50% of infertile couples say that they have sex less than once a week or less and one third say that they have sex less than once a week - often only once a month.
In those who only have sex once a month, sex is usually experienced under pressure for the sole purpose of achieving conception.
Sometimes the man finds this pressure so great that he is unable to achieve an erection.
Even when he can 'oblige' the stress and demand of the moment make pregnancy unlikely.
High levels of stress hormones prevent successful implantation.
I have written an e-book called Making love and babies in which I look at the many factors that contribute to this low level of sexual activity and provide advice.
The problem issues include the age of the couple, the age of the relationship, changes in gender roles that have occurred over the last few decades, the woman's own conflict between the roles of being an independent woman versus a mother, stress itself, long working hours, loss of libido, poor sexual technique and fatigue.
I also look at some of the interesting effects of different foods on brain chemistry and arousal.
Even your diet affects how sexy you feel! I have found some very interesting facts and figures from a wide range of different types of studies that show how the couple is influenced by a large number of things at the same time.
I give advice on how to the effects of many of the conflicting and distracting issues can be reduced.
Better sexual technique is likely to give couples far more enjoyment as well as increasing the likelihood of conception.
There are simple exercises that can be used to increase sensuality and arousal in both partners.
Women enjoy sex much more when their partner has control over the timing of his ejaculation and men can greatly improve their prowess by practising pelvis floor exercises.
Since pelvic floor exercises improve back strength and general body health, this is helpful on all fronts.
Assuming that a couple is fertile, then the frequency of love making is the factor that determines the likelihood of conception.
Put simply, the more sex you have the more likely you are to get pregnant.
But being fertile usually makes both men and women feel more sexy so if you aren't feeling sexy then you might not be fertile.
Fortunately this can also usually be overcome by adopting a healthy lifestyle and reducing stress.
If you are one of these couples where you want to get pregnant but sex itself is a problem then you should work out why so little sex and see whether you can overcome the problem.
The great benefit of overcoming the low or no-sex problem is that life with your partner becomes much more joyful and rewarding.