Seat belts work for everyone, including pregnant women. Like all occupants, they are more likely to be seriously injured if they do not wear seat belts.

A pregnant woman should wear a lap-shoulder belt, and the lap portion should be worn as low as possible, below the rounding, throughout the pregnancy.
The best way to protect the fetus is to protect the mother. When a seat belt is worn properly, it is more likely that the fetus will not be hurt in a crash. For pregnant women, as for anyone, the key to making seat belts effective is wearing them properly.
Lap-Shoulder Belt
Seat Belt ExtenderFastener Tightening Specifications - Seats Seats
Fastener Tightening SpecificationsApplicationSpecificationMetricEnglishFront Seat Mounting Bolt45-Y33-lb-ftFront Seat Adjuster Handle Screw2-Y18-lb-inFront Seat Inner Recliner Finish Cover Side Screw5Y44-lb-inFront Seat Cushion Frame Bolt12-Y9-lb-ftRear Seat Back Cushion Latch Screw2.5-Y22-lb-inRear ...