Firstly dropping HB in such a rapid manner warrants to be investigated further. Just make sure to check all parameters such as MCH, MCHC, MCV as well as platelet, do complete iron studies, folate and
B12 levels, screening for Sickle and Thalassemia based on MCH levels. Once all ruled out then it becomes easier to conclude on iron deficiency. In this case yes you can have a Caesarean section with a HB of 9. Good Luck with your pregnancy. Please make sure to take iron with VIT C related juices like orange or pineapple.