A miscarriage in the second trimester—defined as a pregnancy loss between 13 and 20 weeks—is far less common than a first-trimester loss, but it happens. The causes are often different from early pregnancy losses. While first-trimester miscarriages are frequently due to random chromosomal abnormalities in the embryo, second-trimester losses are more often linked to maternal health conditions, structural problems with the uterus or cervix, or infections. Understanding the specific cause matters because it guides what testing and treatment might follow.
What Is Considered a Second-Trimester Miscarriage?
Healthcare providers divide pregnancy loss into two main categories. Early miscarriage occurs before 13 weeks. Late miscarriage, which is the second trimester, occurs between 13 and 20 weeks. After 20 weeks, a loss is classified as a stillbirth.
Second-trimester losses account for roughly 2-3% of all pregnancies. This makes them much rarer than first-trimester losses, which affect an estimated 10-15% of clinically recognized pregnancies. Because the causes differ, the medical evaluation after a second-trimester loss is more extensive.
What Causes A Miscarriage In The Second Trimester?
The most common causes fall into several categories: cervical insufficiency, uterine abnormalities, placental problems, infections, and maternal medical conditions. Chromosomal abnormalities in the fetus are less common in the second trimester than in the first, but they still account for a meaningful number of cases.
In many cases, no clear cause is found. Studies suggest that even after a thorough evaluation, a specific cause is identified in only about half of all second-trimester losses. This is not a failure of medicine—it reflects how complex pregnancy loss can be.
Cervical Insufficiency (Incompetent Cervix)
Cervical insufficiency is one of the leading causes of second-trimester miscarriage. The cervix is normally a firm, closed structure that holds the pregnancy inside the uterus. In some women, the cervix shortens and opens painlessly before the pregnancy reaches full term.
This is not a sudden event. The process often happens over days or weeks. A woman may notice increased vaginal discharge, pelvic pressure, or a sensation of fullness. Many women have no symptoms at all until the membranes rupture or labor begins.
Risk factors for cervical insufficiency include a history of cervical trauma from a prior difficult delivery, surgical procedures on the cervix such as a cone biopsy or LEEP, and uterine abnormalities. Some women have cervical insufficiency without any identifiable risk factor.
When cervical insufficiency is diagnosed in a current pregnancy, a cervical cerclage—a stitch placed around the cervix—may be offered. Evidence from clinical trials supports its use in women with a history of second-trimester losses due to cervical insufficiency.
Uterine Structural Abnormalities
The shape and structure of the uterus can affect whether a pregnancy can be maintained into the third trimester. A uterine septum, which is a band of fibrous tissue dividing the uterine cavity, is one of the more common structural issues. Other abnormalities include a bicornuate uterus (heart-shaped) or a unicornuate uterus (one-sided).
These structural issues can reduce blood flow to the placenta or limit the space available for the growing fetus. The result may be preterm labor or late miscarriage. A uterine septum can often be removed surgically in a procedure called hysteroscopic resection. This surgery is generally considered safe, and some research suggests it improves outcomes in women with recurrent losses.
Fibroids—noncancerous growths in the uterine wall—can also contribute to second-trimester loss if they are large or located where they interfere with placental attachment or fetal growth. However, most fibroids do not cause pregnancy loss.
Placental Problems
The placenta is the lifeline between mother and baby. When it fails, the pregnancy cannot continue. Two main placental problems cause second-trimester losses: placental abruption and placental insufficiency.
Placental abruption occurs when the placenta separates from the uterine wall before delivery. This can cause heavy bleeding and deprive the fetus of oxygen. Abruption can happen suddenly and is considered an emergency. Risk factors include high blood pressure, preeclampsia, trauma, and cocaine use.
Placental insufficiency is a slower process. The placenta does not deliver enough oxygen and nutrients to the fetus. This is often linked to maternal vascular disease, such as chronic hypertension or a blood clotting disorder. Growth restriction may be detected on ultrasound before the loss occurs.
Infections
Infections are a significant cause of second-trimester miscarriage, particularly between 13 and 20 weeks. The infection may reach the uterus through the cervix or through the bloodstream.
Bacterial infections such as E. coli, Group B Streptococcus, and Ureaplasma can cause inflammation of the fetal membranes, a condition called chorioamnionitis. This inflammation can trigger preterm labor and membrane rupture.
Viral infections can also be responsible. Parvovirus B19, which causes fifth disease in children, can cause severe fetal anemia and hydrops. Cytomegalovirus (CMV) and listeria infections are also associated with late miscarriage. Listeria is a foodborne infection linked to unpasteurized dairy products and deli meats.
Some research suggests that untreated infections of the reproductive tract, such as bacterial vaginosis, may increase the risk of late miscarriage, though the evidence is not conclusive.
Maternal Medical Conditions
Chronic health conditions in the mother can interfere with the pregnancy’s ability to continue. The most important are:
- Thyroid disease: Both untreated hypothyroidism and hyperthyroidism are associated with increased pregnancy loss.
- Diabetes: Poorly controlled pre-existing diabetes increases the risk of miscarriage and fetal abnormalities.
- Antiphospholipid syndrome (APS): This autoimmune condition causes blood clots that can block placental blood flow. It is a well-established cause of recurrent miscarriage, including second-trimester losses.
- Chronic hypertension: High blood pressure before pregnancy increases the risk of placental insufficiency and abruption.
- Kidney disease: Moderate to severe renal impairment is linked to poorer pregnancy outcomes.
Autoimmune diseases such as systemic lupus erythematosus (lupus) also raise the risk, particularly if the disease is active during pregnancy.
Chromosomal Abnormalities in the Fetus
While chromosomal problems are the dominant cause of first-trimester loss, they still account for a significant portion of second-trimester losses. Trisomies—such as trisomy 18 or trisomy 13—are often incompatible with survival to term. These abnormalities are typically random events and not inherited from either parent.
When a second-trimester loss occurs, genetic testing of the fetal tissue can determine whether a chromosomal abnormality was present. This testing is called karyotyping or chromosomal microarray analysis. The results can provide closure and guide recurrence risk counseling.
Blood Clotting Disorders
Inherited thrombophilias—genetic conditions that increase the tendency to form blood clots—have been studied as a cause of pregnancy loss. The evidence is mixed. Some studies suggest a link between certain thrombophilias and late pregnancy loss, but others do not.
Factor V Leiden and the prothrombin gene mutation are the most commonly studied. Testing for these conditions is not routine after a single loss. It is typically reserved for women with recurrent losses or a personal history of blood clots.
Treatment with blood thinners such as low-molecular-weight heparin is sometimes offered, but the evidence supporting this is limited. Clinical guidelines vary on when to treat.
What Testing Happens After a Second-Trimester Loss?
After a second-trimester miscarriage, a thorough evaluation is recommended. This usually includes:
- Genetic testing of the fetal tissue, if available
- Blood tests for antiphospholipid antibodies
- Thyroid function tests
- Blood glucose screening
- An ultrasound to assess uterine structure
- Testing for infections, such as a vaginal swab or blood tests for CMV and parvovirus
An autopsy, if the family consents, can provide information about fetal development and potential causes. Some families decline this, and that is a valid choice. The decision should be discussed with a healthcare provider to understand what information might be gained.
Can a Second-Trimester Miscarriage Be Prevented?
Prevention depends on the cause. When a cause is identified, some interventions may reduce the risk in future pregnancies. A cervical cerclage for cervical insufficiency, surgery for a uterine septum, and treatment for antiphospholipid syndrome are all examples of targeted interventions with evidence behind them.
For many women, no cause is found, and no preventive treatment exists. This is difficult to accept, but it is the honest reality. There is no proven way to prevent a second-trimester miscarriage when the cause is unknown.
Some clinicians recommend progesterone supplementation in women with a history of second-trimester loss, particularly if cervical shortening is detected. Evidence for this is mixed, and it is not a standard recommendation for all women.
Emotional and Physical Recovery
Recovery from a second-trimester miscarriage involves both physical healing and emotional processing. Physically, bleeding and cramping may continue for several weeks. Menstrual periods typically return within 4-8 weeks. A healthcare provider should be consulted if bleeding is very heavy, fever develops, or pain is severe—these can be signs of infection or retained tissue.
Emotionally, grief after a late miscarriage can be profound. Many women have already announced the pregnancy and begun bonding with the baby. Support groups, counseling, and open communication with a partner are all reasonable options. There is no set timeline for grief, and there is no “right” way to feel.
Chances of a Healthy Pregnancy After a Second-Trimester Loss
Most women who experience a second-trimester miscarriage go on to have a healthy pregnancy. The exact likelihood depends on the cause. When a cause is identified and treated, the outlook is generally good. When no cause is found, the recurrence risk is still low for most women.
One study of women with unexplained second-trimester loss found that over 80% achieved a live birth in a subsequent pregnancy. This is reassuring, but it is not a guarantee. Each pregnancy is different, and close monitoring in a subsequent pregnancy is often recommended.
Frequently Asked Questions
Can stress cause a second-trimester miscarriage?
No direct evidence shows that everyday stress causes a second-trimester miscarriage. Severe physical trauma can, but psychological stress alone has not been proven to cause late pregnancy loss.
How common is a second-trimester miscarriage?
Second-trimester miscarriage affects roughly 2-3% of pregnancies. This is much less common than first-trimester loss, which occurs in about 10-15% of recognized pregnancies.
What are the warning signs of a second-trimester miscarriage?
Warning signs include vaginal bleeding, cramping, back pain, fluid leakage, and a decrease in fetal movement. These symptoms do not always mean a miscarriage is happening, but they require prompt medical evaluation.
Can a second-trimester miscarriage happen without bleeding?
Yes. Some losses are discovered on ultrasound after the fetal heartbeat has stopped, without any prior bleeding. This is called a missed miscarriage and can occur at any gestational age.
