Despite the shrill admonitions of the ''lifestyle'' brigade, most problems in pregnancy are not caused by the woman. Our chief enemy is the powerful and merciless adversary we face daily, ''Mother Nature''.

Despite the unpredictability of it all, there are recognisable patterns in human pathology, and known risk factors that signal a higher chance of things going wrong. Doctors should educate people so they may do what they can to minimise the chance of adverse events when possible.

In the case of pregnancy, increased maternal age is a major risk factor. Firstly, fertility declines rapidly with age. IVF has a ''take home baby'' rate of 3 per cent at age 42 in most units. The rate of most pregnancy problems, medical, obstetric and foetal, rises from the late 20s, and dramatically from age 35 onwards. Although any woman may miscarry, it is well known that the rate is age dependent, being about 14 per cent at 27, rising to 40 per cent at 40, and more than 60 per cent at 45. A similar rise with age is seen in the risk of birth defects and chromosomal abnormalities, of diabetes and high blood pressure in pregnancy, of caesarean delivery and its complications, of premature birth, of handicapped infants, and of medical problems such as thrombosis, heart, kidney and thyroid problems, cancers and depression.

Considering all these and other medical problems, and obstetric problems dealt with by obstetricians and midwives such as haemorrhage, out of 100 women age 28 who conceive today, no more than 70 will experience an uncomplicated pregnancy, delivery and postnatal period. At age 42, only about 27 will avoid complications.

My responsibility is to interpret the body of knowledge for my patients and others. No one need take my advice, but in good conscience I cannot retreat from giving the counsel I believe is correct. In many cases involving older women with medical problems, particularly when they already have children, I have advised against pregnancy. In too many of these, I have suffered with the parents as they cuddle a lifeless bundle in a hospital room that would usually be filled with joy. Too often I have seen maternal mortality or life-threatening illness, both catastrophes, particularly when existing children are left motherless and would not have been so had the couple left the family as it was. Was their decision to risk a pregnancy selfish? Others can judge.