First things first- labor & delivery is generally reserved for patients actually in labor. You won't generally be rounding on them in the morning in the traditional sense. While on your OB block, you'll likely be responsible for rounding on patients on the postpartum or antepartum units.
For your postpartum patients important parts of the exam (beyond the basics) are the incision if they had a c-section, the location of the uterine fundus, and any signs of DVT since the highest risk of a blood clot is after delivery.
For antepartum patients you may be asked to listen for fetal heart tones. And again, the risk of DVT is high so check for that. Other specifics depend on the reason the patient is hospitalized-- checking for fundal tenderness in PPROM patients, reflexes/clonus in pre-eclamptics, CVA tenderness in pyelo, etc.