Miscarriage during the first trimester is more common than many people realize.

A first trimester miscarriage refers to the loss of a pregnancy during the first 13 weeks of gestation. According to the American College of Obstetricians and Gynecologists (ACOG), about 10-15% of known pregnancies end in miscarriage, and the majority occur during the first trimester.

The most common cause of first trimester miscarriage is chromosomal abnormalities 

The leading cause of first trimester miscarriage is chromosomal abnormalities in the embryo. Research shows that roughly half to two-thirds of early miscarriages are linked to missing or extra chromosomes. 

Chromosomes carry the genetic instructions needed for development. When an egg and sperm combine, the embryo may end up with the wrong number of chromosomes (extra or missing) and errors can occur during cell division. The body naturally recognizes the abnormalities and prevents the embryo from developing further. These genetic errors are usually random and are not inherited from the parents. Common chromosomal-related miscarriages include:

• Anembryonic pregnancy (blighted ovum) – the gestational sac develops, but the embryo does not.
• Intrauterine fetal demise – the embryo develops initially but stops growing.
• Molar pregnancy – abnormal placental tissue forms instead of a viable pregnancy.

Other causes of miscarriage during the first trimester

While about 50% or more of early miscarriages can be traced to chromosomal issues in the developing embryo, there can be many other reasons that it can occur. Other contributing factors may include maternal age, underlying health conditions, uterine abnormalities, and certain lifestyle risks.

• Maternal Age – As maternal age increases, the risk of chromosomal abnormalities also rises due to age-related changes in egg quality. By age 40, the risk of miscarriage rises to 40% and by age 45 it may reach as high as 80%.
• Hormonal and Medical Conditions – Certain underlying health conditions can interfere with a healthy pregnancy and increase the likelihood of miscarriage. These can include uncontrolled diabetes, thyroid disease, hormonal imbalances, obesity, and infection. Proper prenatal care and management of chronic conditions can help reduce risk.
• Uterine or Cervical Problems – Structural abnormalities in the uterus may make it difficult for an embryo to implant or grow normally. These can include uterine fibroids, uterine structural issues such as a septum, abnormally shaped uterus, and incompetent cervix.
• Lifestyle and Environmental Factors – Certain lifestyle habits are linked with a higher miscarriage risk, especially when exposure is significant. Risk factors include smoking, heavy alcohol use, illicit drug use, excessive caffeine intake, and environmental exposure to harmful chemicals or high levels of radiation may also increase risk in some cases.

What doesn’t cause a first trimester miscarriage?

It is essential to separate myths from facts. First, early pregnancy loss is generally a random, unpreventable event. Activities such as moderate exercise, working, emotional stress, or sexual intercourse are not considered typical causes of miscarriage in healthy pregnancies.

Further, having one miscarriage does not necessarily mean future pregnancies will fail. Most people who miscarry later go on to have healthy pregnancies. Generally, if you experience recurrent miscarriages, two or more consecutive ones, this may be a sign of an underlying genetic, hormonal, or anatomical issue that deserves medical evaluation. 

Final thoughts on miscarriage during the first trimester 

First trimester miscarriage is unfortunately very common. And while the grief associated with losing any pregnancy is real, the important thing to remember is that a first trimester loss is rarely caused by routine actions or personal mistakes. Understanding the medical realities behind miscarriage can help reduce stigma and self-blame while encouraging compassionate support for those affected.