During Pregnancy:
It is safe to have sex throughout pregnancy, As long, as there are no complications, such as vaginal bleeding or any other complications. If there are any, or you suspect that there may be any complications, you should contact your doctor or midwife immediately.

As pregnancy progresses couples may have to experiment with positions which will maximize the woman’s comfort, and allow her to control the amount of penetration. If she is experiencing any discomfort the use of a lubricant might be helpful.

After Child Birth:
There is no set rule for this, although MEDICALLY, it is safe to resume sex after six weeks after delivery.

How ever, one needs to take into consideration vaginal tenderness, and sex that would mutually satisfying and pleasurable

All in all, one needs to consider how the new mother is feeling. There are too many influences and emotions to take into consideration. Be patient, and loving. Try and give your wife a break, some time to herself, to relax and exercise.