I'm not sure of the procedures used in the U.S for obstetrics, I'm sure they are vastly different where I am. I would look up the meds used in Obstetrics such as Oxytocin, think its called Pitocin in the U.S, drugs used for pain releif in labor. You could look at disorders of pregnancy and labor and what meds are used for these. Probably Pre eclampsia, pre labour rupture of membranes, preterm birth, prolonged labor, PPH, APH, and Gestational diabetes seem to be pretty much global concerns. That will lead you to look up the corresponding medications such as corticosteroids, magnesium sulphate, insulins used in pregnancy (there is a really good research article on the use of Metformin in pregnancy), antibiotics, RhoGram (anti D), antihypertensives that are used in pregnancy and ones that are contraindicated (ACE inhibitors & Beta Blockers are CI in pregnancy). There is also the meds used to induce labor that you might like to read up on.
Probably looking at the physiology of pregnancy would be helpful, there are lots of changes. Women have physiological anaemia because of haemodilution, and also have a drop in b.p during the first trimester usually reaching pre pregnancy levels during the 2nd to 3rd trimester. So you might like to look at the Hb levels, and why the anaemia occurs and at what levels is something done about it.
You might like to look at the different stages of labor, and how to assist the woman in active first stage. Honestly there is a lot of information, I think you could just read up on what you are interested in at this stage and I'd probably start with the physiological changes during pregnancy then concentrate on the disorders and the meds used for them.