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Why do miscarriages usually happen?

Miscarriage refers to the loss of a fetus before the 20th week of pregnancy. Nearly one million women in the US suffer miscarriage every year. With miscarriage being so common and painful to handle, it is advisable to understand the risk factors of miscarriage. It will not only help prevent it but also ensure your well-being. Let us discuss the causes below.

1. Abnormal development of a fetus

 It is one of the primary reasons for miscarriage during the first trimester. Several factors including genetic issues contribute to a miscarriage within the first 90 days. The chromosomal defects in the fetus cause errors to occur erratically during the division of fetal cells. Damaged sperm or egg cell could also cause such abnormalities. Types of chromosomal problems include the following.

Blighted Ovum: One of the reasons for early miscarriage, it refers to the lack of development of an embryo after implantation. Abdominal cramps and heavier periods than usual are its common symptoms. 

Complete molar pregnancy: Although rare, it occurs when a sperm with no genetic information fertilizes an egg. The placenta grows abnormally and appears swollen with fluid-filled cysts. Its symptoms include dark brown to bright red vaginal bleeding during the first trimester, severe nausea and vomiting, and pelvic pressure or pain.

Partial molar pregnancy: When two sperms fertilize an egg, thus disturbing the genetic make-up of an embryo, it causes partial molar pregnancy. Placental abnormalities, abnormal fetus, and grape-like cysts are its common signs. Its symptoms are similar to that of complete molar pregnancy but may also include high blood pressure during the first trimester of pregnancy.

The intrauterine demise of the fetus: It generally occurs after the 20th week of pregnancy and refers to the death of the fetus in the uterus. Some of its causes include post-term pregnancy (passing 42 weeks of gestation), chronic maternal disorders (e.g., high blood pressure, diabetes, or obesity), or maternal infections (for example, malaria, COVID-19, toxoplasmosis, syphilis, etc.). The most common symptoms of IUDF include lack of fetal movement, pain and cramping, and vaginal bleeding.

2. Physical complications

Physical health problems with the mother may cause a miscarriage, more so in the second or third trimester. For example, uterine fibroids adversely affect implantation or blood flow to the fetus. Septum, a rare uterine defect in women, has also been linked to miscarriage. Scar tissue in the uterus because of surgery or second-term abortions also harms pregnancy by preventing proper implantation of an egg and disrupting the blood supply to the placenta. In most cases, gynecologists detect uterine defects through specialized X-rays before the pregnancy or during its initial stages to minimize the risk of miscarriage. 

3. Hormonal Imbalances

Less production of the hormone progesterone in a woman’s body may also cause miscarriage. Progesterone strengthens the uterine lining to support the fetus and helps the placenta take hold. Insufficient production of progesterone is common in women who have suffered multiple miscarriages. Treatment may improve the chances of a successful successive pregnancy.


Polycystic ovary syndrome (PCOS) causes multiple cysts in the ovaries. It is one of the primary reasons for infertility in women because it reduces the production of eggs. PCOS-led pregnancy complications include early loss of pregnancy, preeclampsia, and gestational diabetes. The odds of miscarriage are three times higher in women with PCOS. Some research shows that metformin may mitigate the risk of miscarriage in expectant women with PCOS.

5. Incompetent cervix

Also known as cervical incompetence, it refers to weakened cervical muscles that cannot hold the fetus. It may occur because of an injury or after surgery. When the fetus grows a bit by the second trimester, the weak muscles may cause the cervix to open too early, thus resulting in miscarriage.

6. Long-term health conditions

The following health conditions of the mother may also cause miscarriage. 

  • uncontrolled diabetes
  • hypertension
  • thyroid disease
  • heart disease
  • antiphospholipid syndrome
  • immune system disorders such as lupus
  • kidney disease
  1. Other risk factors

Besides health problems, a few other factors that increase the likelihood of miscarriage include:

  •  age- women aged 35 and above may have an increased risk of miscarriage. When you are 35 years old, the risk of miscarriage is about 20 percent; it increases to 40% at age 40, and to 80% when you are 45.
  • weight- Obesity increases the risk of miscarriage by 73%. Being overweight or obese increases insulin resistance. It also alters the levels of androgen and estrogen and makes BMI higher. All of these are physiological links to miscarriage. 
  • smoking- First and second-hand smoking is detrimental to the health of both mother and baby. The dangerous chemicals in cigarettes increase the likelihood of early miscarriage and stillbirth. It also interferes with the growth and function of the placenta and the development of the fetus.
  • alcohol and drugs- Drinking alcohol or taking drugs when pregnant may lead to miscarriage. Period. Abstaining from drugs and alcohol consumption is the only way to women’s wellness during pregnancy. In addition, moderate to heavy drinkers are at a greater risk of giving birth to a baby with physical deformities and intellectual disabilities.
  • food poisoning- Eating contaminated or raw foods also contribute to the likelihood of miscarriage. For example, listeriosis found in unpasteurized dairy products triggers inflammation in the mother’s body. It impairs the ability of the placenta to protect and nourish the fetus. Eat hygienically prepared, well-cooked, and nutritious food during pregnancy. Wash fruits and veggies thoroughly before consumption. If you think you are allergic to anything, you may consult your doctor and take a few tests to detect the cause.
  • trauma- Depending upon the stage of pregnancy and the severity of the accident, physical or mental trauma may lead to miscarriage. So, better be safe than sorry. Avoid heavy exercises, walk carefully, and drive cautiously. As much as possible, keep stress to the minimum. 

The first step to preventing miscarriage is knowing its causes. Hope you found this blog helpful.

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