Causes of Miscarriage in the Second Trimester

A miscarriage in the second trimester is a pregnancy loss that happens specifically between 12 and 20 weeks of gestation. (After this time, the loss is more accurately classified as a stillbirth or neonatal death.) No matter the timing, it's only natural to want answers when such an event occurs.

Causes of second-trimester miscarriage vary, but, in most cases, the pregnancy loss isn't due to anyone's actions. Oftentimes, even your doctor won't be able to explain why it happened.

Chromosomal Abnormalities

Chromosomal abnormalities, such as trisomies, are a major cause of almost all forms of pregnancy loss. Second-trimester miscarriages are caused by these abnormalities about one-quarter of the time. Prenatal testing may have made you aware of the potential for this, but that is not always the case.

Unlike a first-trimester pregnancy loss, second-trimester miscarriages are less likely to be caused by a chromosomal abnormality. All told, around a third of second-trimester losses are a result of genetic aberration.

Congenital Defects

.Congenital birth defects are those that are often inherited but may also be caused by an infection during pregnancy or exposure to certain teratogenic (defect-causing) medications, chemicals, or toxins. Birth defects such as heart or brain malformations in your developing baby can make your pregnancy a nonviable one.

Depending on the type and severity of the birth defect, your doctor may be able to diagnose any potential problems via ultrasound. Others may be detected during routine prenatal screenings.

Placental Problems 

One such problem is called a placental abruption. If your placenta—the structure that's attached to the wall of the uterus and gives nutrients to your baby via the umbilical cord—suddenly peels off the wall of the uterus before you're ready to give birth, this can prevent your developing baby from getting necessary nutrients and oxygen.

Symptoms of placental abruption include vaginal bleeding, abdominal pain, uterine contractions, cramping, and back pain during the last 12 weeks of pregnancy.

Cervical Insufficiency

Cervical insufficiency, also known as an incompetent cervix, means your cervix is weak and begins dilating and opening too soon. Some women experience cervical insufficiency after having a challenging birth or after having a cervical procedure performed like loop electrosurgical excision procedure (LEEP), laser ablation, or cold knife conization. Others develop the condition due to congenital uterine malformations.

Symptoms of cervical insufficiency include backache, vaginal bleeding, abdominal cramps, pelvic pressure, and vaginal discharge, usually between 14 and 20 weeks of pregnancy.


Uterine infection is another possible cause of miscarriage, although it is a more common cause in developing countries than the United States. With that said, any untreated or severe uterine infection may trigger the spontaneous loss of pregnancy, including:

  • Bacterial vaginosis
  • Candida (yeast) infections
  • Chlamydia
  • Gonorrhea
  • Trichomoniasis
  • Viral vaginitis

Poorly Controlled Chronic Conditions

Chronic diseases in the mother can also increase the risk for pregnancy loss. In many cases, the risk increases if the disease is poorly controlled with medications or lifestyle. Other chronic conditions carry an inherent risk of pregnancy loss depending on their severity. Examples include:

The risk can be further increased in women who smoke, are obese, or have hormone problems.


Thrombophilia is an increased risk of forming blood clots in blood vessels like veins and arteries that may be due to a genetic abnormality or a problem with your immune system, such as in lupus. This can cause problems involving your placenta and your umbilical cord. Thrombophilia is sometimes treated during pregnancy with blood thinning drugs or with low-dose aspirin.

Symptoms of thrombophilia include pain, swelling, and tenderness in your leg (usually in your calf) as well as red or warm skin (particularly at the back of your leg below the knee).

Abdominal Trauma 

Any trauma such as an automobile accident, fall, or being hit in the abdomen can hurt both you and your developing baby and potentially cause a miscarriage.

In a car, always wear a seat belt, placing the lap belt under the uterus and putting the shoulder strap between your breasts. Avoid high-impact physical activities that might cause you to lose your balance. Try not to let your kids roughhouse with you, if you can avoid it.

If you are a victim of domestic violence, call 1-800-799-SAFE, the National Domestic Violence Hotline.

Drug and Alcohol Use

Cocaine and methamphetamine are especially linked to miscarriage. Studies have shown that the use of illegal drugs has been associated with low birth weight, premature labor, placental abruption, and fetal death. Alcohol has also been cited as a cause of pregnancy during not only the first trimester but the second trimester as well.

According to research from the University of Copenhagen, light drinking (defined as one to two drinks per week) increases the odds of an early second-trimester miscarriage by 70 percent.

Unknown Causes

Sometimes a pregnancy loss occurs for no apparent reason and, no matter how much a doctor investigates, no cause can be found. As distressing as this may be, it does happen and more frequently that one might think.

Moreover, having had a prior second-trimester miscarriage in and of itself is a risk factor for subsequent second-trimester miscarriages. While the cause may be identified in some women (like cervical insufficient or uterine defects), others will remain a mystery.

According to research from the University of Pennsylvania, women with a prior second-trimester miscarriage were 10.8 times more likely to have recurrent second-trimester losses compared with women who previously delivered at term.

A Word From Verywell

If you've had second-trimester pregnancy loss and are pregnant again, consult your doctor early in your pregnancy in case extra monitoring may be needed. A miscarriage of a prior pregnancy doesn't necessarily mean that a woman is at high risk, as most women go on to have healthy pregnancies.

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