Pre-existing illness: cannot only affect a pregnancy, it can also be affected by the pregnancy. Rheumatic diseases such as rheumatoid arthritis in general improve during the course of a pregnancy, though they can flare up after the baby is born. Cardiac disease, since the demands on the heart increase, can worsen, and women with a history of heart disease need optimum medical and cardiological care. Inflammatory bowel disease, as with other inflammatory conditions, usually improves while thyroid disorders - whether overactive or under active - require increased treatment. Epilepsy needs careful monitoring during the course of the pregnancy, since too little treatment will cause convulsions, while too much can affect the foetus.

With any chronic disorder the aim is to maximise and maintain the health of the mother without adversely affecting the development of the foetus (which may be at risk both from the disorder and from the treatment) - this requires the co-ordinated attention of those skilled both in the disorder, and the effects of pregnancy.