If you were under the care of a gynecologist during your pregnancy, many more than three ultrasounds were often performed without prior information about possible risks. Also, 3D/4D souvenir photos or DVDs were made.
Why was this changed?
Research has been able to demonstrate in animal studies, among other things, cell changes and damage, as well as problematic cell heating when ultrasound is used. Unborn children are to be protected. Legislators have therefore decided to reduce the use of ultrasound on the unborn child. The protection of the unborn child is given priority because there is no proof that ultrasound waves are harmless.(1)

Weighing up the advantages and disadvantages.
Ultrasound also offers advantages as a method of examination. That is why three voluntary "basic ultrasounds" continue to be paid for by health insurance companies. If this results in a photograph, it is not prohibited. International health authorities have agreed that ultrasounds should be infrequent and as brief as possible. Only ultrasound for which there is no medical indication is affected by the new regulation. Additional ultrasound with a medical indication will continue to be paid for by health insurers.

For which medical indications can an additional ultrasound be necessary?
For example: in case of bleeding, unclear pain or other complaints to which no cause can be assigned without ultrasound.

It must be documented that you have been informed and have given your consent.
You are giving consent on behalf of your child, who is not yet capable of giving consent.

We recommend that you limit yourself to a maximum of two basic ultrasound examinations (in the 2nd and 3rd trimesters of pregnancy). Based on scientific research, we do not recommend using ultrasound to determine pregnancy or to determine the date of birth. Midwives and physicians determine both even without technical aids.