First of all, it should be clear that a surrogacy pregnancy works like any other pregnancy, and as such it involves the same medical risks. In addition to the most common pregnancy symptoms, some serious side effects include gestational diabetes, hypertension, etc. Also, there is also the risk of miscarriage or preterm labor, aspects that should be properly envisaged in the surrogacy contract.
In gestational surrogacy, the are also some medical risks and side effects associated with IVF. Whether it is the intended mother or an egg donor who contributes the eggs, injecting herself with fertility medications can lead to some adverse reactions, such as allergy or slight needle bruising.
The gestational carrier can experience cramping or bleeding from the embryo transfer procedure as well. Although rarely, there is also some risk of developing an infection. In such case, treatment with antibiotics would be necessary.
Finally, if multiple embryos are transferred, it is likely that the GC gets pregnant with twins or even triplets, which at the same time increases the likelihood of preterm labor, C-section, placental abruption... To reduce the risks associated, GCs should follow their doctor's recommendations strictly.