What Causes Second Trimester Miscarriages?

The Many Possible Causes of Second Trimester Miscarriages

pregnancy ultrasound
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Experiencing a pregnancy loss in the second trimester may take you by surprise because it's not very common. There is just a 1% to 5% chance of it happening, according to the March of Dimes.

What Is a Second Trimester Miscarriage?

Technically, a second trimester miscarriage is a pregnancy loss that happens specifically between 12 and 20 weeks. A pregnancy loss after 20 weeks (when you're halfway along) would not be classified as a miscarriage.

It would be labeled a stillbirth or a neonatal death.

A number of factors can lead to a second trimester miscarriage. Some miscarriages that are diagnosed early in the second trimester might have actually occurred in the first trimester, but were not detected immediately (these are called missed miscarriages).

Causes of Second Trimester Miscarriage

Miscarriages that occur after 12 weeks of gestation can be due to chromosomal abnormalities, which are a major culprit in almost all forms of pregnancy loss. But second trimester miscarriages are more likely to be caused by other factors. Some of these include:

Cervical insufficiency: This means that 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 LEEP, laser ablation, or a cold knife conization. Others develop the condition due to congenital uterine malformations.


Infections: A uterine infection, for example, is one possible cause, though this is more common in developing countries, compared with the U.S. 

Abdominal trauma: Perhaps you got into an automobile accident. Or maybe you tripped and fell down hard onto your stomach area. Your toddler jumped onto your belly.

Or perhaps you were the victim of a domestic violence incident during which a loved one hit or kicked you in the mid-section. These are all examples of abdominal trauma that 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. And if you're a victim of domestic violence, call 1-800-799-SAFE, the National Domestic Violence Hotline, immediately.

Congenital birth defects: These may include heart malformations in your developing baby.

Thrombophilia: This 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. This can cause problems involving your placenta and/or your umbilical cord. About 20% of women have thrombophilia.

Thrombophilia is sometimes treated during pregnancy with blood thinning drugs and/or with low-dose aspirin. 

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 either a little bit or completely before you're ready to give birth, this can prevent your developing baby from getting necessary nutrients and oxygen.  

Unknown causes: Sometimes none of the above is at play, and the true trigger simply remains a mystery. 

Women who have had second trimester pregnancy losses should consult with a doctor early in their next pregnancies in case extra monitoring is needed.


March of Dimes, "Miscarriage." June 2005. Accessed 15 Feb 2008.

Miscarriage Association, “Late Miscarriage.” Accessed 15 Feb 2008.

"Understanding Second Trimester Pregnancy Loss." Department of Obstetrics and  Gynecology, UC Davis Health System.

Murry, RN, CNM, Mary, "Don't ignore abdominal trauma while pregnant." Mayo Clinic (2009).

Danielsson, Krissi, "Thrombophilia - A Common Source of Multiple Miscarriages," (2016). 

"Placental abruption definition." Mayo Clinic (2014).

"What is the placenta?" National Health System (2015).

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