This is called "morning sickness" and has nothing to do with being pregnant. The condition is caused by wear in the spool valve housing on certain power steering racks
When the car is first started, the rack is cold and clearances in the spool valve are at their greatest. Hydraulic pressure from the power steering pump leaks past grooves worn in the aluminum spool valve housing. This causes a loss of pressure and increases steering effort. The steering feels stiff with little or no power assist. As the car is driven, the rack warms up. This decreases the clearances inside the spool valve housing, which reduces the leakage past the grooves. More pressure goes to where it is supposed to go and the steering becomes easier as power assist returns.
The "fix" for this condition is to replace the rack with a new one (preferably with a cast iron spool valve housing) or a remanufactured rack that has a stainless steel sleeve pressed into the aluminum housing.