When Rachel is seeing her doctor, you can see up the sleeve of her gown to see that she's wearing a red top underneath. When wearing a hospital gown, a patient is usually naked underneath or at most wear a bra.
As Rachel starts leaving Monica's apartment in her body-revealing top, a piece of equipment can be seen behind her.
Rachel becomes pregnant shortly before Monica and Chandler's wedding, which is May 15th (according to 'The One With the Cheap Wedding Dress') - this would put her due date somewhere around December or January. However, as Rachel nears her due date she is dressed for summer weather and talks about it being "100 degrees" outside.