Our four-year-old son wets his bed at least once a week. We have tried rewarding him for not doing so, restricting fluids before bedtime and waking him in the night, but it hasn't worked. What can we do?
First you must accept he is not to blame in any way, and that around one in five four-and-a-half year-olds bed-wet once a week or more. Don't restrict his fluids: he needs enough fluids throughout the day. And instead of rewarding him for a dry bed (he can't control whether or not his bed will be dry), praise him for using the toilet several times in the day – four to seven times is usual. Don't get him up in the night – all that does is disturb his sleep. Be patient and talk over the subject with your doctor, who will put you in touch with a health adviser. If it continues beyond the age of five, you may be offered an alarm system or a drug called desmopressin, but you are a long way from that. Above all, don't show anger or anxiety when the bed is wet.

Is it true that you are more likely to have severe pregnancy sickness if you are carrying a girl than if it's a boy? A friend told me that it's because we have higher circulating oestrogen levels if we are expecting a girl.
Intuitively this would appear to be reasonable, and many women anecdotally have found they were sicker with girls than with boys – but you can't depend on anecdotal evidence, I'm afraid. In my years of caring for pregnant women before we had scans to determine the sex of their babies, this was one of the commonest questions they asked. Were they more sick with girls? In general, they may have been, but too many were just as sick with boy babies for a reliable prediction. Morning sickness starts very early in pregnancy, often before the baby's hormone levels become significant in comparison with her mother's, so initially there shouldn't be a connection. However, if the sickness continues beyond the 16th week or so, when the baby's hormone patterns are established, gender may come into consideration, and may be part of the reason for the sickness lasting longer than usual, but it isn't the whole story, as many mothers of boys will testify.

• Do you have a question for Dr Smith? Email doctordoctor@theguardian.com