All things being equal (which they never are), it is better to avoid x-rays while pregnant.

If indicated, (chronic cough, possible fracture, etc.), then x-rays are acceptable.

If you need an x-ray for a pregnant patient, go ahead and get it, but try to shield the baby with a lead apron to minimize the fetal exposure.

In your zeal to shield the pregnant abdomen, be careful not to shield so much that the value of the x-ray is diminished. If the shielding is too high while obtaining a chest x-ray, you will have to obtain a second x-ray to visualize the area shielded during the first x-ray.

The risk to the fetus from radiation exposure is minimal in these circumstances. There appears to be a threshold for fetal malformation or death of at least 10 Rads, below which, biologic effects cannot be demonstrated. Allowing for a 10-fold margin of safety, it does not appear that any exposure below 1 Rad will have any harmful effects.

It would take about a thousand chest x-rays to deliver this amount of radiation to the unshielded maternal pelvis. 

At the same time, our knowledge of the biologic effects or radiation may be incomplete, so it is better for pregnant women, as a rule, to avoid any unnecessary exposure to ionizing radiation, and to use appropriate shielding when it is necessary.