Miscarriage risk factors: what raises the chance

What a miscarriage is

NICHD defines pregnancy loss as the unexpected loss of a fetus before the 20th week of pregnancy. It is also called miscarriage, early pregnancy loss, mid-trimester pregnancy loss, fetal demise or spontaneous abortion. A loss after 20 weeks is called stillbirth (NICHD).

Pregnancy loss may happen so early that a woman may not know she was pregnant. NICHD cites an American College of Obstetricians and Gynecologists estimate that early pregnancy loss is common, occurring in about 10% of confirmed pregnancies (NICHD). MedlinePlus says most miscarriages happen very early in the pregnancy (MedlinePlus).

Why it happens

MedlinePlus says a miscarriage can happen in any pregnancy, and most occur because the fetus doesn't develop properly, often because of a genetic problem such as an extra or missing chromosome (MedlinePlus). NICHD says the number of chromosomes the fetus has, too many or too few, can affect survival (NICHD).

Other possible causes NICHD lists (NICHD):

• Being exposed to toxins in the environment
• Problems of the placenta, cervix or uterus
• Problems with the father's sperm

Both sources stress that the cause is often not known. NICHD says that in many cases health care providers can't identify a cause, sometimes even after additional tests (NICHD). MedlinePlus says miscarriage can affect anyone and often can't be prevented (MedlinePlus).

What raises the chance

NICHD lists these risk factors (NICHD):

• Older age of the parents. Chromosome problems happen more often in the fetuses of older parents, particularly women older than 35, so the risk rises with age; it is much higher at 45 than at 35.
• Previous miscarriages. Women who have had them are at higher risk.
• Chronic diseases such as high blood pressure, diabetes, thyroid disease (see hypothyroidism) or polycystic ovary syndrome (PCOS).
• Immune system problems, such as an autoimmune disorder.
• Infections, such as untreated gonorrhea (see chlamydia and gonorrhea screening) or Zika.
• Hormone problems.
• Extremes in weight, such as obesity or being too thin (see the BMI calculator).
• Lifestyle factors: using drugs or alcohol, smoking (see the quit smoking check), or having more than 200 milligrams of caffeine a day, about one 12-ounce cup of coffee.

MedlinePlus gives a similar list of factors that may increase the chance: problems with the uterus or cervix, chronic diseases including PCOS, genetic problems with the fetus, pregnancy after 35 years of age, smoking, drug or alcohol use, chronic conditions such as uncontrolled diabetes, and severe malnutrition (MedlinePlus).

NICHD also notes research linking morning sickness (nausea and vomiting in pregnancy) with a lower risk of pregnancy loss (NICHD). Neither source gives a score.

Signs of a miscarriage

NICHD lists these symptoms (NICHD):

• Bleeding from the vagina
• Pain or cramps in the lower stomach area (abdomen)
• Low back pain
• Fluid, tissue or clot-like material coming out of the vagina

MedlinePlus adds dark-colored vaginal discharge (MedlinePlus). Bleeding does not always mean a miscarriage: many pregnant women have spotting and cramping in early pregnancy and do not miscarry, and some women have no symptoms of pregnancy loss at all (NICHD).

Although this is rare in the United States, NICHD says some women who have a miscarriage get an infection in the uterus, which can be life threatening. It lists these symptoms as reasons to call 911 (NICHD):

• A fever higher than 100.4 degrees Fahrenheit on more than two occasions
• Severe pain in the lower abdomen
• Bloody discharge from the vagina, which can include pus and be foul smelling

Diagnosis, treatment and afterward

To check for a miscarriage, a provider may do a pelvic exam, blood tests and an ultrasound. Early in pregnancy no treatment may be needed. At 12 or more weeks, a shot may be needed to prevent problems with the Rh factor in future pregnancies (see Rh(D) screening in pregnancy). If tissue remains in the uterus, options include waiting for it to pass, medicines, or a procedure such as dilatation and curettage (D&C) or vacuum aspiration (MedlinePlus).

MedlinePlus says losing a pregnancy can be difficult and counseling may help with grief. Many women who have a miscarriage go on to have healthy pregnancies later; if you plan to try again, talk with your provider about any risks. It advises taking good care of yourself and starting prenatal care visits early (MedlinePlus).

Related pages

An ectopic pregnancy is a different kind of pregnancy loss that always needs treatment; see ectopic pregnancy risk factors. For births before 37 weeks, see preterm birth risk factors.

Common questions

Did I cause my miscarriage?

Most miscarriages happen because the fetus doesn't develop properly, often because of a chromosome problem, and the cause is often unknown (MedlinePlus). MedlinePlus says miscarriage often can't be prevented. Your provider can talk through your own situation.

How common is miscarriage?

NICHD cites an estimate of about 10% of confirmed pregnancies, and says the true number is hard to know because some losses happen before a pregnancy is confirmed (NICHD).

Does age raise the risk of miscarriage?

Yes. NICHD says the risk rises as parents age, particularly for women older than 35, and is much higher at 45 than at 35 (NICHD).