Hello and welcome to MedHelp's forums. Thank you for your question and congratulations on the pregnancy. Please do consult with her doctor about this as your best source of information that is directly in relation to your wife's health history. In general though, a drop in hemoglobin during pregnancy is normal and often happens. However, a significant drop can be more alarming. Here is an article that describes anemia (low hemoglobin) in pregnancy. https://www.medicinenet.com/anemia_in_pregnancy/views.htm. If your wife started the pregnancy with low hemoglobin which can happen if her period prior to becoming pregnant was heavy, it makes it more pronounced and problematic during the pregnancy. I do want to also point out that anemia also increases as pregnancy continues from the first to third trimester. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4779156/. This article talks more about anemia in pregnancy.
Now I believe you are saying your wife's hemoglobin is at 7.7. If it drops to 7 or below, then her doctor will likely take further action such as a blood transfusion. How is her B12? That should also be looked at. Hopefully her doctor has a plan to help increase her hemoglobin. Again, she needs to be eating iron rich foods such as leafy green vegetables, dried fruit, etc.
We, again, encourage you to work with your doctor on this issue. Please let us know how she is doing.