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What is a miscarriage?

A spontaneous abortion (SAB), or miscarriage, is the most common type of pregnancy loss. The medical term for a miscarriage is "spontaneous abortion" (SAB). A miscarriage (or spontaneous abortion) is a pregnancy loss that ends without intervention, surgery, or medication. 
There is no clear consensus as to the exact pregnancy week when a miscarriage is defined, but most agree it's usually before the 20th week of pregnancy. A "stillbirth" is the death of a fetus after 20 weeks of pregnancy.

Types of miscarriages

There are several types of miscarriage – threatened, inevitable, complete, incomplete, or missed. Then there are also other types of pregnancy loss such as ectopic, molar pregnancy, and a blighted ovum.

An ectopic pregnancy happens when the embryo implants outside the uterus, usually in the fallopian tube or other places. And ectopic usually ends with an early pregnancy loss. Technically, an ectopic pregnancy is not a "miscarriage", though similar to a miscarriage it is an early pregnancy loss.

How often does a miscarriage happen?

Miscarriages occur in up to 50% of all known pregnancies. A miscarriage is a common, though often difficult, and often painful part of pregnancy.  Studies show that many early miscarriages happen before the mother realizes she was pregnant (chemical pregnancy) and experts estimate that about half of all fertilized eggs die and are miscarried, usually even before the woman knows she is pregnant. Between 10-25% of all clinically recognized pregnancies will end in miscarriage, and most miscarriages occur before the 7th and 12th weeks of pregnancy.

Early pregnancy loss

In the first trimester, before 13 weeks of the pregnancy, the terms miscarriage, spontaneous abortion, and early pregnancy loss are used interchangeably, and there is no clear consensus as to which term to use. Early pregnancy loss is common. It occurs in 10% of all clinically recognized pregnancies, and the vast majority of about 80% of all cases of pregnancy loss occurs within the first trimester. It includes the loss of the early pregnancy, including probably a blighted ovum, a molar pregnancy, and an ectopic pregnancy.

Chemical pregnancy

chemical pregnancy is a pregnancy with a positive pregnancy test but no visible pregnancy on ultrasound. Chemical pregnancies may account for 50-75% of all miscarriages. It occurs when a pregnancy is lost shortly after implantation, resulting in bleeding that occurs around the time of or shortly after her expected period. Unless there was a positive pregnancy test, the woman may not realize that she conceived when she experiences a chemical pregnancy.

Induced abortion

Abortion is commonly used to describe the intentional ending of a pregnancy. However, medically speaking, an abortion could be the unintentional ending of pregnancy (as a miscarriage or spontaneous abortion) or the intentional ending of pregnancy (induced abortion).

Miscarriage symptoms and signs

No woman or couple wants to think about the chance of a miscarriage, but a large percentage of pregnancies end before full gestation. Understanding the most common miscarriage symptoms is the best way to be prepared for the chance of miscarriage. Pregnancies are different for every woman and as such, miscarriage symptoms may also be different. Some women know from the start that the pregnancy is just “not right” and others who are taken by complete surprise by the miscarriage symptoms.

Lower abdominal cramping

Early miscarriage symptoms may start as a pain in the lower abdomen similar to menstrual cramping. The pain may stay the same during the miscarriage or could increase in intensity to the point where medical attention is sought. Any form of cramping during pregnancy (especially if it's associated with red bleeding) should be immediately reported to the obstetrician.

More than just spotting

Spotting is common during the first month of pregnancy, but spotting is different from bleeding. Miscarriage symptoms are commonly combined so the cramping may start at the same time as vaginal bleeding. If blood is bright red and flowing like a menstrual cycle, immediately head to the emergency room. Active vaginal bleeding during pregnancy is not normal at any time.

Septic miscarriage

Not every miscarriage starts with bleeding and cramping. In some cases, the miscarriage starts an infection in the uterus, which leads to vaginal discharge. The vaginal discharge will be thick, possibly yellow or greenish, and have a strong smell. Other septic miscarriage symptoms include fever, lethargy, fatigue, and chills. Even if you think the symptoms are associated with the flu or common sinus infection, they can be life-threatening if attributed to a septic miscarriage, so seek emergency medical attention right away.

Loss of pregnancy

The most difficult miscarriage symptoms to notice are a lapse of pregnancy symptoms. During the first few weeks of pregnancy, breasts will be tender and morning sickness may begin. If these symptoms suddenly stop, they could be considered miscarriage symptoms. Pregnancy symptoms are attributed to estrogen levels in the body and when a miscarriage starts, estrogen levels may quickly return to normal. When this happens, the body no longer “feels” like it is pregnant.

Types of miscarriages

Miscarriage is often a process and not a single event. There are many different stages or types of miscarriage. Most of the time all types of miscarriage are just called a miscarriage, but you may hear your health care provider refer to other terms or names of miscarriage such as:

Threatened miscarriage

Some degree of early pregnancy uterine bleeding accompanied by cramping or lower backache. The cervix remains closed.

Incomplete miscarriage

Abdominal or back pain accompanied by bleeding with an open cervix. Miscarriage is inevitable when there is a dilation or effacement of the cervix and/or there is a rupture of the membranes. Bleeding and cramps may persist if the miscarriage is not complete.

Complete miscarriage

A completed miscarriage is when the embryo or products of conception have emptied of the uterus. Bleeding should subside quickly, as should any pain or cramping. A completed miscarriage can be confirmed by an ultrasound or by having a surgical curettage performed.

Missed miscarriage/missed abortion

It is possible to experience a miscarriage without even knowing it. A missed miscarriage is when embryonic death has occurred but there is not any expulsion of the embryo. Signs of this would be a loss of pregnancy symptoms and the absence of fetal heart tones found on an ultrasound.

Many people are confused by the word 'abortion' in the term 'missed abortion'. As a result, the term is no longer commonly used. A missed abortion is more frequently referred to today as a delayed or silent miscarriage. This means that the embryo is no longer living (or was never fully formed), though the body has not yet shown signs of miscarriage. It is only classified in this manner, however, if it occurs before the 20th week of pregnancy.

There are a few reasons why a missed abortion may occur. The majority of cases are thought to be due to abnormalities during cell division, though not much is known as to why this happens. A blighted ovum, which is where an egg is fertilized with the placenta and no embryo, is another cause for this condition. The other cause is a molar pregnancy, which is where the cells in the placenta grow out of control, creating a massive cyst. In both of these cases, the embryo cannot survive.

There are a few ways that a missed miscarriage can be handled. One is to allow it to run its course and allow the body to naturally expel the embryo or fetus. The other option is to have a D&C procedure to get rid of the tissue. (See an ultrasound of a missed abortion.)

Recurrent miscarriage/pregnancy loss

Defined as 3 or more (some consider 2 or more) consecutive first trimester miscarriages. This can affect 1% of couples trying to conceive. Recurrent pregnancy loss (RPL), habitual or recurrent abortions or miscarriages are diagnosed when three or more miscarriages occur in a row. About 5% of couples have two miscarriages in a row, and up to 2% have three miscarriages or RPL in a row.

"Primary recurrent pregnancy loss" refers to couples that have never had a live birth, while "secondary RPL" refers to those who have had repetitive losses following a successful pregnancy.
There are many known causes for RPL, however, there is a significant number of couples in whom even after a thorough workup, no specific cause is found.

In a couple with RPL, many doctors usually perform most, if not all, of the following procedures:

  • Evaluation of ovarian reserve (LH, FSH, estradiol on CD 3)
  • Evaluation for uterine anomalies (Sonogram, hysterosalpingogram)
  • Genetic evaluation of both partners (Chromosome karyotyping)
  • Hormone evaluation (Progesterone after ovulation, endometrial biopsy)
  • Evaluation of autoimmune problems (Lupus screen, ANA, anticardiolipin antibody, factor V Leiden, APPT)

According to the American College of Obstetricians and Gynecologists, cultures for bacteria and viruses, glucose tolerance testing, thyroid tests, antibodies to infectious agents, anti-thyroid antibodies, paternal human leukocyte antigen status, or maternal anti-parental antibodies are not beneficial and, therefore, are not recommended in the evaluation of otherwise normal women with recurrent pregnancy loss.

In this 2021 study, taking baby aspirin in the preconception period, before and during pregnancy, resulted in improved pregnancy outcomes with fewer miscarriages.


It's important to remember that about 95% of women who have one miscarriage will conceive again and give birth.

Why does a miscarriage occur?

A miscarriage, also referred to as a spontaneous abortion, occurs in many pregnancies. Typically, a miscarriage happens before the end of the first trimester, but it can happen at any time up to 20 weeks. After 20 weeks, the loss of a pregnancy is considered a preterm birth.

Studies show that up to 50% of pregnancies end in miscarriage before the mother realizes she was pregnant. Between 10-25% of all clinically recognized pregnancies will end in miscarriage, and most miscarriages occur before the 7th and 12th weeks of pregnancy.

Odds of a miscarriage

  • No increased risk if just one prior miscarriage
  • 1 in 4 after 2 consecutive clinical losses
  • 1 in 3 after 3 consecutive clinical losses
  • 1 in 2 of all (including 'subclinical'=chemical) pregnancies
  • 1 in 5 in clinical pregnancies (early pregnancy is seen on ultrasound)
  • 1 in 10 after 7 weeks with a positive fetal heartbeat
  • 1 in 25 after 12 weeks with a positive fetal heartbeat
  • 4 in 5 miscarriages happen before 12 weeks
  • There is a 2 in 3 risk that a miscarriage is due to chromosome problems
  • There is a 4 in 5 risk that a miscarriage is due to chromosome problems if the prior miscarriage was due to chromosome problems
  • Less than 1 in 20 chance that a miscarriage is due to a hormone deficiency (for example, progesterone problems)

Predicting a miscarriage

According to findings presented at the American College of Obstetricians and Gynecologists (ACOG) 57th Annual Clinical Meeting, a successful pregnancy can be predicted with up to 94% accuracy between days 33 and 36 after conception using transvaginal ultrasound to detect 3 markers:

  • Yolk Sac (2-6 mm over 90% success)
  • Gestational Sac (over 12 mm: 92% success)
  • Fetal Heartbeat (over 90% success)

Second-trimester miscarriage

In most cases, the signs of miscarriage will appear in the first trimester. The common belief is that if a woman makes it through the first trimester she is safe with a small chance of miscarriage. This does not mean a miscarriage will not occur later in pregnancy. Signs of miscarriage in the second trimester may include some of the early signs of miscarriage, but there are a few that are specific to late-stage miscarriage.

Ruptured membranes

By the second trimester, the membranes protecting the baby are in place. If a woman feels fluid leaking from the vagina or her bag of water ruptures, this is a clear sign of miscarriage or early labor. It may not be a gush of fluid as is represented in Hollywood movies. Instead, women more commonly feel just a small trickle of fluid similar to urination. If any tissue or grayish material is passed, collect it and immediately take the tissue to the hospital.

Missing heartbeat

If the doctor cannot find a heartbeat in the second trimester during a regular doctor’s visit or as part of an emergency visit it could be one of the signs of miscarriage. At times, the heartbeat can be difficult to find with a Doppler handheld unit, but an ultrasound will verify the missing heartbeat.

Pregnancy after miscarriage

Yes, many women can conceive after a miscarriage. About 95% of women who have one miscarriage will conceive again and give birth. Even women who have more than one miscarriage have a 75% chance of achieving a full-term pregnancy. In some cases, increasing viability of full-term gestation may require medications to boost HCG or progesterone, but this is not always the case.

Women are most fertile in the time immediately following a miscarriage, but most obstetricians and gynecologists will suggest waiting until the first normal menstrual cycle has passed before trying to conceive again. In some cases, doctors suggest waiting six months or more before trying to conceive, but this depends on the reasons for the miscarriage and the common practices of the attending physician.

Miscarriage is more common than many women understand. Just because a miscarriage occurs, women are not necessarily less likely to conceive and achieve motherhood. It is best to work with the attending Ob-Gyn to maximize the chance of carrying the fetus to term after a miscarriage.

How long to wait after a miscarriage 

The female body is ready to conceive again immediately after a miscarriage. Hormone levels are at their highest, so infertility is reduced and fertility increased. However, for the sake of the female body and reducing the chance of a second miscarriage, many doctors will suggest waiting for at least one regular menstrual cycle to increase the chances of getting pregnant and maintaining the pregnancy. Other doctors will suggest waiting up to six months to increase the chances of getting pregnant without complications.

The chances of achieving pregnancy after a miscarriage are often the same as they are before the miscarriage. Women, who try for a second pregnancy, tend to be successful 95% of the time. Women with two or more miscarriages have a success rate of 75% on subsequent tries. Health, illnesses, disease processes, and other contributing factors will affect the chances of getting pregnant, more than a miscarriage. However, it is important to note that some women are more likely to have miscarriages for unknown reasons. Testing does not always determine a cause for miscarriages.

Read More:
What Causes A Miscarriage At Six Weeks?
What Is a Chemical Pregnancy?
How Often Does Miscarriage Happen?