Pregnant women experience surges in progesterone and estrogen hormone levels that occasionally cause them to experience chills. More typically these hormonal surges cause heat flushes and sweating, as Parents magazine explains.
Another possible reason a pregnant woman may experience chills without a fever is when the woman has a thyroid imbalance, which is often first noticed and diagnosed during her pregnancy. A thyroid problem can be confirmed with a blood test. Most typically, however, chills indicate the presence of an infection; kidney infections are particularly common during pregnancy, according to Parents magazine. When caused by an infection, the chills are likely to be accompanied by fever and possibly by nausea.