First things first, are you certain you are miscarrying? Why is your doctor so sure you are miscarrying? Is it because there is an empty sac? If so, my first question is whether or not your gestational sac is growing and if it is more that 25mm (see New Blighted Ovum Guidelines! Chances Are You ARE Being Diagnosed Too Soon!).
If there are serious complications, ending your pregnancy right away may be necessary (i.e. infection setting in, ectopic, molar pregnancy, etc...). If your doctor does believe there is a serious complication but you are not convinced, you may decide to seek a second opinion but, please, do it right away.
Serious complications aside, do you need to have the D&C right away? Let's see what the American Pregnancy Association says:
"About 50% of women who miscarry do not undergo a D&C procedure. Women can safely miscarry on their own, with few problems in pregnancies that end before 10 weeks. After 10 weeks, the miscarriage is more likely to be incomplete, requiring a D&C procedure to be performed. Choosing whether to miscarry naturally (called expectant management) or to have a D&C procedure is often a personal choice, best decided after talking with your health care provider."Please take note:
"Women can safely miscarry on their own, with few problems in pregnancies that end before 10 weeks."The takeaway is this: If you are not 100% certain of your miscarriage diagnosis and there are no complications -or- even if you are certain and would prefer to miscarry on your own, waiting for a natural miscarriage is an option many women choose. You should not feel pressured to have a D&C if you do not want one. You can always choose to have the D&C at a later point. You should not feel rushed.
After ten weeks, miscarriages may become more complicated and a D&C may be the safest way to go. Talk to your doctor and the two of you can determine your best course of treatment.
As always, seek a second opinion if you are at concerned that your diagnosis might not be an accurate one. This isn't false hope. This is just being 100% certain before you end your pregnancy.