What Are the Common Causes of Miscarriages?

Friendly doctor holds patients hand after helping her through a miscarriage.

The first question many couples and single people ask themselves after experiencing a miscarriage is why? There are countless reasons why you may have a miscarriage in your life, and most of them are beyond your control.

In many cases, particularly with early miscarriages, it can be hard to determine what went wrong. You have two sets of genetic material coming together that must divide, and sometimes things go wrong. The simplest way to think about it is that a miscarriage is nature’s way of ensuring that a human being is compatible with life.

While many people who suffer a miscarriage blame themselves, the truth is that they’ve probably done nothing to cause it. Here’s everything you need to know about the reasons for miscarriages and a few helpful tips to reduce your risk of having one!

Chromosomal Abnormalities

When a miscarriage happens in the first 12 weeks of pregnancy, more than half the time, it’s because of a problem with the baby’s chromosomes. Chromosomes contain the genes that determine your baby’s unique traits, such as hair and eye color. A baby can’t grow normally with the wrong number of chromosomes or damaged ones.

Miscarriages caused by chromosomal abnormalities happen more often in women older than 35. This is because all the eggs that a woman will ever have are present from birth, and the eggs age with her. The frequency of miscarriage in women below age 20 is around 12 to 15 percent and doubles as the woman approaches age 40. Nothing can be done to prevent miscarriage due to a chromosomal abnormality, and once a miscarriage has begun, there is nothing one can do to stop it.

Medical Conditions

A pregnancy loss often results from a problem with the mother’s health. Some of these include:


Women with diabetes need to work with their primary care physician or endocrinologist to optimize their sugar control. Uncontrolled insulin-dependent diabetes in the first trimester can lead to increased miscarriage rates and an increased risk of major birth defects.

Thyroid Disorders

Thyroid disorders can lead to problems with infertility or cause recurrent miscarriages. In cases where a woman’s thyroid function is low, her body will try to compensate by producing hormones that can suppress ovulation. Conversely, a thyroid that is producing too many hormones can interfere with estrogen’s ability to do its job, making the uterus unfavorable for implantation or leading to abnormal uterine bleeding.

Blood Clotting Disorders

Like physical abnormalities, miscarriages from blood clotting disorders such as Factor V Leiden are rare, but they do occur. Clotting issues that block blood vessels carrying blood flow to the placenta are a major concern.


Having a sexually transmitted disease such as chlamydia, gonorrhea, syphilis, or HIV during pregnancy can bring an increased risk of miscarriage, stillbirth, preterm delivery,​ and other maternal and fetal complications. It’s also possible for an infection to pass to a baby in the womb or during labor, and even during breastfeeding. 

Hormonal Imbalances

Sometimes a woman’s body doesn’t produce enough of the hormone progesterone, which is necessary to help the uterine lining support the fetus and help the placenta take hold. Medication may improve the odds of a successful subsequent pregnancy, but doctors don’t often test for this unless a woman has had multiple miscarriages.

How to Decrease Your Risk of a Miscarriage

In many cases, miscarriage can’t be prevented, especially when the cause is chromosomal abnormalities that aren’t compatible with life. Still, doctors advise optimizing your health before you conceive to give your pregnancy the best fighting chance.

  • Give up tobacco, alcohol, and any illegal drugs.
  •  Keep conditions such as diabetes or high blood pressure under control.
  • Keep your weight within a healthy range.
  • Get on a schedule of regular prenatal visits. You may need to go for more frequent checkups to monitor your pregnancy.
  • Discuss the timing of your next pregnancy with your doctor. Some recommend waiting a certain amount of time (from one menstrual cycle to 3 months) before trying to conceive again.
  • Stay active. If your healthcare provider gives you the thumbs up, incorporate gentle exercise into your healthy pregnancy plan.

Keep in mind that repeated miscarriage is the exception, not the rule. Only about 1% of couples have two or more miscarriages in a row. Most of the things that cause miscarriage are beyond your control, so it’s important to discuss your next steps with your doctor.

At South Avenue Women’s Services, we provide women with the compassionate health care they deserve. From gynecological exams to sexually transmitted disease testing to safe abortion procedures, we have the knowledge and experience to help you make the best decisions for your body.

Contact us today at (585)271-3850 to schedule an appointment with a trusted women’s health care professional!