The second half of the infertility definition (the one that’s talked about much less) is the inability to remain pregnant. People who are able to get pregnant but have experienced recurrent pregnancy loss often see fertility specialists, but it’s a complex issue—some of the reasons for pregnancy loss, especially early on, are related to fertility, but some are totally unrelated.

According to the American Society for Reproductive Medicine (ASRM), 15–25% of pregnancies end in miscarriage—but the actual number is likely higher, because many miscarriages occur so early that the person doesn’t yet know they’re pregnant.

The vast majority of people who experience a miscarriage will go on to have a healthy pregnancy and birth. Two or more consecutive miscarriages is known as recurrent miscarriage or recurrent pregnancy loss, experienced by less than 5% of pregnant people.

Identifying the cause of pregnancy loss

The potential causes of a pregnancy loss change based on when in the pregnancy the loss occurs—we’ll go over the different stages below. But it’s important to know that in many cases, healthcare providers aren’t able to identify with certainty a cause or “diagnosis” for a miscarriage.

Secondly, it’s important to understand that, in the majority of pregnancies that end in miscarriage, it’s not due to something the pregnant person did or didn’t do. The term “miscarriage” may seem to imply some mistake on the part of the person carrying, but that’s not the case; while pregnancy loss can be devastating, it’s important (and factually accurate!) not to blame yourself.

In the majority of pregnancies that end in miscarriage, it’s not due to something the pregnant person did or didn’t do.

What doesn’t cause pregnancy loss: exercise, including high-intensity activities like running or cycling, or sexual intercourse. And except in cases in which a pregnant person works with harmful chemicals or radiation, working outside the home does not increase the risk of miscarriage. Finally, there’s no evidence that normal stress, anxiety, or mild depression can cause miscarriage.

Early pregnancy loss (first trimester)

First-trimester losses comprise upwards of 75% of all miscarriages.

Abnormal chromosomes

Most miscarriages, especially early ones, occur because the fetus isn’t developing normally; up to 70% of early miscarriages demonstrate extra or missing chromosomes. Chromosomal abnormality can be due to egg or sperm quality, but can also happen spontaneously as the embryo divides.

Because older eggs are more likely to have chromosomal abnormalities, a mother’s age is number one variable associated with miscarriage. Mothers under 35 have a 15% chance of miscarriage, mothers ages 35–45 have a 20–35% chance of miscarriage, and mothers over age 45 have up to a 50% chance of miscarriage. There’s also evidence that the chance of miscarriage increases with paternal age, especially when the female partner is older than 35.

Chemical pregnancy

A “chemical pregnancy” is an early miscarriage that occurs shortly after implantation, and may account for over half of all losses according to the American College of Obstetricians and Gynecologists (ACOG). In the case of a chemical pregnancy, you may have a positive pregnancy test—indicating the presence of hCG (human chorionic gonadotropin), a pregnancy hormone the embryo creates after implantation—but the embryo doesn’t develop. Sometimes this is diagnosed after the hCG levels don’t increase as they normally should.

Late pregnancy loss (second trimester)

As a pregnancy progresses, the chance of miscarriage drops significantly, and the potential causes of loss change. Pregnancy losses that occur in the second trimester or later are less likely to be related issues of fertility, including sperm or egg quality.


A viral, bacterial, or fungal infection in a pregnant person can cause histologic chorioamnionitis (HCA), infection and inflammation of the placenta. HCA may also be caused when the amniotic sac (the “water”) breaks too early. In one study, HCA was found in 67% of second trimester pregnancy losses.

Listeriosis, an infection caused by the listeria bacteria sometimes found in lunch meat and soft cheese made with unpasteurized cheese, can also cause miscarriage. While the infection is rare overall, pregnant people are 10–20 times more likely to get listeriosis than non-pregnant people. Listeriosis can affect fetal health at any time during pregnancy and can also cause early labor and neonatal illness.

Cervical insufficiency

Cervical insufficiency, also known as cervical incompetence, is a condition in which the cervix—the “neck” of tissue connecting the uterus to the vagina—begins to dilate (widen) and efface (thin) before the pregnancy is complete. Experts estimate that approximately a quarter of second trimester losses can be attributed to cervical insufficiency. In most cases, it’s unknown what’s caused the condition.

Uterine abnormalities

As the pregnancy progresses and the fetus grows, abnormalities that affect the uterus’ ability to expand may impact the health of the pregnancy.

It’s estimated that 8–23% of people experiencing recurrent pregnancy loss have a uterine abnormality, such as a septate uterus (a uterus with a band of tissue down the middle). These abnormalities are congenital and may not be identified or diagnosed until pregnancy.

Additionally, large fibroids—benign tumors in the uterus—can cause miscarriage in rare cases. Learn more about uterine fibroids and fertility.

Chronic illness

Two types of chronic illnesses in a mother are known to impact fetal and pregnancy health: diabetes and autoimmune disorders.

If diabetes is not well controlled, blood sugar levels may become too high, which is unhealthy for a developing fetus. A pregnant person who isn’t carefully managing their diabetes has a higher chance of having a miscarriage or stillbirth.

In some autoimmune disorders, such as antiphospholipid syndrome and lupus, there’s the presence of “antiphospholipid antibodies.” These antibodies mistakenly attack a type of fat—phospholipids—and associated proteins that line the blood vessels, and are associated with an increased risk of miscarriage and recurrent pregnancy loss, as well as blood clots. Medications that help prevent blood clots, such as aspirin and heparin, have been shown to be effective treatments for autoimmune-related recurrent pregnancy loss.

Fetal loss (after 20 weeks)

Also known as fetal demise/death or stillbirth

Loss at any stage of pregnancy can be very difficult, but loss after 20 weeks is particularly devastating. It’s important to note that stillbirth is rare, affecting about 1% of all pregnancies.

Often, no cause can be identified; in one study 60% of fetal losses were unexplained. Stillbirths are less commonly a result of genetic abnormalities. Approximately 15% of fetal deaths are related to birth/genetic defects, as opposed to over half of early miscarriages. Infections are still possible after 20 weeks, and in one study were responsible for 17% of fetal deaths.

Placental problems

Problems with the placenta, the organ that develops with and nourishes the fetus, account for approximately a quarter of fetal deaths after 20 weeks. Placental abruption is the most common problem; in this condition, the placenta separates from the inner wall of the uterus before birth, which can deprive the fetus of oxygen and nutrients and cause heavy bleeding in the mother. While abdominal trauma can bring on placental abruption, in most cases there’s no identified cause. Pregnant people over 40 have an increased risk of placenta-related fetal loss.

Problems with the umbilical cord

A small percentage of fetal deaths can be attributed to the umbilical cord, the fetus’ source of oxygen, becoming knotted or squeezed. This tends to occur toward the end of a pregnancy, when the fetus is large enough to create pressure on the cord.

Next steps after pregnancy loss

It’s important to know that pregnancy loss doesn’t mean you’ll never be able to have children. Most people who have experience a miscarriage can and will go on to give birth to a healthy baby. And even if pregnancy loss is recurrent (less than 5% of cases), there are still treatment options.

In addition to being fertility experts, a reproductive endocrinologist—like the doctors on our team—is often the specialist (or are part of the team) that treats recurrent pregnancy loss.

Treatment for recurrent pregnancy loss

The right treatment for RPL depends on the cause and the nature of the loss. Deciding on and undergoing a treatment should only be done in close conversation with your doctor.

IVF with preimplantation genetic screening (PGS)

PGS is a process by which an embryo created during IVF is genetically tested prior to transfer to the uterus. PGS can help reduce the chance of miscarriage by ensuring that the embryos transferred are genetically healthy; as discussed above, approximately half of early miscarriages are due to genetic abnormalities.

Implementation of PGS has been shown to signficantly reduce the chance of miscarriage for older pregnant people from 39% to 2.7% (in one study) and to increase the per-cycle chance of a live birth and reduce the time and number of cycles required to achieve a live birth (in another).

Here’s how PGS works: after creating embryos in the lab with IVF, an embryologist will perform an embryo biopsy, a procedure in which a few cells are taken from the embryo and sent to a genetics lab for testing. Then, all the embryos are cryogenically frozen while the testing is performed. The lab will report back on which embryos contain the correct number of chromosomes (46). Then, the healthy embryo(s) can be thawed and used during a frozen embryo transfer.

Learn more about IVF with genetic testing here at Extend Fertility.

Surgery to correct a uterine abnormality

In the case of congenital uterine anomaly or large fibroids, surgery is the best bet to improve a patient’s chances of live birth.

Low-dose daily aspirin and/or heparin

For those who have experienced recurrent miscarriage in relation to an autoimmune disease, taking a low-dose aspirin—sometimes known as a “baby” aspirin—daily may be recommended. Heparin, a blood thinner, has also been shown to be very effective in reducing the chance of recurrent miscarriage. In one review, it was determined that treatment with heparin and aspirin together may reduce the chance of miscarriage by 54%.