Some women prefer natural miscarriage because they want to avoid medical intervention and prefer to miscarry in the privacy of their homes without the ordeal of checking into a hospital or having an invasive medical procedure like a D&C. Individuals may have extremely strong preferences in this respect, and most doctors will respect a woman's wish to avoid a D&C.
For most women, choosing to avoid a D&C is probably safe as well. Studies suggest that roughly 70 to 80% of women who wait for a natural miscarriage will be able to do so without unexpected complications. A natural miscarriage is more likely to be free of complications if the pregnancy loss happens before 10 weeks of gestation.
Obviously in certain situations -- like a ruptured ectopic pregnancy or a woman bleeding profusely from a miscarriage -- surgery can be lifesaving and miscarriage treatment does not involve any options. In miscarriages without a medical emergency, usually natural miscarriage does not carry major risks to the woman's health (or else her doctor would recommend another option). A minor risk exists of hemorrhage and or infection, but the risk is similar to a D&C. Studies do show a greater number of unplanned hospital admissions for women who choose natural miscarriage, and women who choose natural miscarriage may end up needing or wanting a D&C later if the tissue from the pregnancy does not leave the uterus in a reasonable amount of time.
Where It Stands
For women who choose a natural miscarriage, what to expect physically may depend on the specifics of the situation. In a very early miscarriage, the miscarriage will look and feel physically like a heavy, crampy menstrual period - possibly with more clots than usual and a slightly longer bleeding time. In a later first-trimester miscarriage, the cramps could be anywhere from mild to severe and the woman might pass recognizable tissue, such as a gestational sac or partially developed embryo or fetus (the term for the developing baby).
Natural miscarriages may have an uncertain timeline. In "missed" miscarriages, a woman could have no miscarriage symptoms and no signs of vaginal bleeding, but an ultrasound reveals a baby with no heartbeat and/or without the expected development. In these cases, the miscarriage bleeding could take anything from hours to weeks to begin - and the wait may be hard to take emotionally. In contrast, if a miscarriage is already in progress when diagnosed, such as if a woman sees her doctor to investigate heavy first-trimester vaginal bleeding, the entire physical process of the miscarriage could be completed in days.
Beside the timeline, different women have different experiences with the duration of bleeding. In most cases, the bleeding from a natural miscarriage should stop entirely within two weeks and should be heavy only for a few days. Longer bleeding times could be a sign that some of the pregnancy tissue is still in the uterus, so this should definitely be reported to a doctor. Severity of cramping also varies among women -- some may have mild or nonexistent cramping whereas others have extremely painful cramps associated with the miscarriage (a doctor can recommend pain medication in these cases).
Levels of hCG (human chorionic gonadotropin), the primary pregnancy hormone, should return to zero within a few weeks after diagnosis of a miscarriage. Doctors sometimes advise waiting a period of time before trying again to get pregnant after a miscarriage but a doctor may also say that a couple can try to get pregnant again as soon as they feel ready.
American Pregnancy Association, "Miscarriage." Jul 2007. Accessed 2 Jan 2008.
Sotiriadis, Alexandros, George Makrydimas, Stefania Papatheodorou, and john P.A. Ioannidis. "Expectant, Medical, or Surgical Management of First-Trimester Miscarriage: A Meta-Analysis." Obstetrics & Gynecology 2005. 1104-1113. Accessed 23 Dec 2007.