Appendix operation done in childhood should not interfere with pregnancy at all. If there are extensive adhesions (due to scarring following the surgery and healing) there may be a problem in case the lady requires a surgery for delivery(caesarean section); otherwise there should not be a problem during pregnancy. Past surgery (in childhood) certainly has no bearing on the fetal growth. I cannot understand why bed-rest has been prescribed. In a healthy pregnant woman it is not required and can be harmful and an appendix in childhood does not make the current pregnancy at risk. Bed-rest sounds like a compassionate advice and most lay people (and indeed some doctors)think it is good for pregnancy and at least harmless. It is based on a presumption that a pregnant woman is a patient. Both these notions are incorrect. A pregnant woman is not a patient (the very fact that she is pregnant proves that she is healthy) and not all patients do well with bed rest. Bed-rest is a significant alteration in life style. Not only is it useless in pregnancy, it is actually quite harmful as women on bed-rest are more likely to have a low birth weight baby and are more likely to require an operative delivery like a caesarean section / forceps / vacuum etc. I do not know why your wife has been prescribed bed-rest so please clarify with your doctor if there is any other problem with her. The pregnant woman should be allowed to do whatever she likes during pregnancy and indeed moderate exercise during pregnancy is both good for the mother and the baby and is harmless.
There is nothing to suggest that physical activity can harm a fetus in any way. For advice regarding activity work and exercise during pregnancy please read Antenatal Care for the Patients (guidelines issued in October 2003 by the Royal College of Obstetrics and Gynaecology, RCOG at www.rcog.org.uk in the 'Good Medical Practices' column) and this will give you a complete picture on modern antenatal care.
Sex during pregnancy is normal and there is no evidence to suggest that it harms the fetus. Indeed there is some evidence that it may be good for the fetus. Endorphins are morphine-like substances released in the body and make us feel good whenever we indulge in a pleasurable activity. Endorphins are good for the pregnancy as they improve circulation (improves blood supply to the placenta) and promote fetal growth. The single largest amount of endorphin release is during sex. Endorphins relieve stress and that is good for the mother and the baby. Earlier it was thought that orgasm may cause premature labour but there is no evidence of that in a normal healthy woman. Nipple stimulation in late pregnancy can cause uterine contractions in people prone to premature labour and should probably be avoided in these cases but in normal healthy women sex is healthy up-to any stage she finds acceptable. Most women have a loss of sex drive in early pregnancy so obviously it should not be forced but if the woman wants it and likes it there is no medical reason not to have sex at any stage during pregnancy. In later pregnancy the position may have to be modified considering the sheer size of the woman's abdomen. You can get some idea about convenient positions during sex from books on the subject like 'Pregnancy' by Gordon Bourne and Everywoman' by Derek Lewellyn Jones.