Overview
Fail pregnancy, also known as miscarriage, is unfortunately quite common and occurs in about 10-20% of all pregnancies. The main causes of miscarriage include:
- Chromosomal abnormalities – About 50% of early miscarriages are caused by chromosomal issues in the fetus that prevent normal development.
- Hormonal problems – Issues with hormones like progesterone can prevent the pregnancy from progressing.
- Uterine or cervical problems – Abnormalities in the structure of the uterus or weaknesses in the cervix can make miscarriage more likely.
- Chronic conditions – Diseases like diabetes, thyroid disorders, or autoimmune issues increase miscarriage risk.
- Lifestyle factors – Smoking, drug use, malnutrition, and excessive caffeine intake are linked to higher rates of miscarriage.
- Infections – Certain bacterial, viral or parasitic infections can cause inflammation that leads to pregnancy loss.
- Age – Miscarriage rates steadily rise as women get older, especially after age 35.
While the exact cause often can’t be pinpointed, the most common factors that can result in fail pregnancy are explored in more detail below.
Chromosomal Abnormalities
Experts estimate chromosomal abnormalities cause about 50-60% of early miscarriages. These occur when there is an error in the number or structure of chromosomes in the embryo created during fertilization.
A normal embryo should have 23 pairs of chromosomes (46 total). But sometimes eggs or sperm have the wrong number of chromosomes, causing issues once they combine. The most common chromosomal defects behind miscarriage include:
- Trisomy – An extra chromosome, resulting in 47 total chromosomes instead of 46.
- Monosomy – A missing chromosome, resulting in 45 chromosomes instead of 46.
- Partial trisomy or monosomy – Having an extra or missing part of a chromosome.
- Triploidy – The embryo gets an extra set of chromosomes from one parent, resulting in 69 chromosomes instead of 46.
These chromosomal abnormalities cause errors in cell division and growth that make it impossible for the embryo to develop normally. The pregnancy ends in miscarriage because the embryo simply cannot survive.
Genetic screening of the embryonic tissue can identify whether chromosomal defects caused a miscarriage. Some women may be more prone to producing eggs or sperm with abnormal chromosomes, especially as they get older. But in many cases, the chromosomal error is a random event that is unlikely to recur in a subsequent pregnancy.
Hormonal Imbalances
Hormones like estrogen and progesterone play key roles in supporting pregnancy. Low levels of these hormones can prevent the endometrium (uterine lining) from developing properly to sustain the embryo. Luteal phase defects cause the corpus luteum in the ovary to produce insufficient progesterone in early pregnancy. This hormonal imbalance is estimated to be responsible for 20-40% of early miscarriages.
Other hormonal problems like polycystic ovarian syndrome (PCOS), uncontrolled diabetes, or thyroid disorders can also make miscarriage more likely if the woman’s hormone levels are not optimized around the time of conception. Tests for fertility hormones and early monitoring of progesterone levels in pregnancy may help identify a hormonal cause. If found, this may be treatable with progesterone supplements.
Uterine or Cervical Abnormalities
Structural or developmental problems in the uterus or cervix can make it difficult for a pregnancy to proceed. Examples include:
- Uterine septum – a wall of tissue dividing the uterine cavity in two.
- Bicornuate uterus – a heart-shaped uterus with two chambers.
- Weak cervix (cervical insufficiency) – the cervix opens early in pregnancy causing premature labor.
- Fibroids or polyps – benign growths in the uterine wall that can interfere with implantation.
- Scar tissue in the uterus – from prior procedures like dilation and curettage (D&C) or cesarean section.
An abnormally shaped uterine cavity may prevent an embryo from properly implanting and growing. Cervical insufficiency also causes miscarriage later in the first trimester as the uterus cannot stay closed.
Uterine defects are often detected only after recurrent pregnancy loss when further testing is done. Surgical repair can help correct some anatomical issues and improve the chances of a successful pregnancy.
Chronic Medical Conditions
Having certain chronic medical conditions increases the risks of miscarriage through various mechanisms.
- Diabetes – Uncontrolled blood sugar causes cell damage and hormonal dysregulation that can prevent embryonic development and implantation. Miscarriage risks are 2-3 times higher with diabetes.
- Thyroid disorders – Both hypothyroidism and hyperthyroidism cause hormone level fluctuations that interfere with fertility and early pregnancy. Women with thyroid issues have double the risk of miscarriage.
- Autoimmune diseases – Antiphospholipid syndrome, rheumatoid arthritis, and lupus cause abnormal immune responses that increase chances of blood clots, poor implantation, or rejection of the embryo in the womb.
- Kidney disease – Reduced kidney function can lead to hormonal imbalances and uterine blood flow changes that threaten the pregnancy.
Testing for such conditions and controlling them with medications and lifestyle changes helps lower, but not eliminate, the added risks to pregnancy.
Lifestyle Factors
A woman’s behaviors and exposures can also influence miscarriage risks. Some key lifestyle considerations include:
- Smoking – Doubles the miscarriage risk by reducing uterine blood flow and causing DNA damage to eggs and embryos.
- Alcohol and drug use – Causes similar damage and chemical exposures that disrupt embryonic development.
- Caffeinated drinks – Excess intake has been associated with higher risk of miscarriage when more than 2 cups per day.
- Poor diet and obesity – Can contribute to problems like diabetes, high blood pressure, and inflammation that threaten pregnancy.
- Environmental toxins – Certain chemicals, heavy metals, and radiation sources may increase the risk.
- Extreme physical exertion – Potentially reduces uterine blood flow for the embryo when done at excessive levels.
While risks can never be eliminated fully, addressing these lifestyle factors helps create the healthiest environment possible for pregnancy. This is especially key for couples with unexplained recurrent losses.
Infections
Maternal infections that spread to the uterus or embryo itself will trigger miscarriage in some cases. Bacteria most often implicated include:
- Listeria
- Salmonella
- Brucella
- Mycoplasma
- Chlamydia
- Gonorrhea
Viral infections like cytomegalovirus (CMV), rubella, and herpes simplex can also prompt pregnancy loss by disrupting fetal development or causing severe placental inflammation.
Malaria and toxoplasmosis parasites represent key parasitic culprits that prompt the immune system to reject the pregnancy to contain the threat.
Testing can identify if infectious causes may explain a miscarriage. Preventative antibiotics may then be used in subsequent pregnancies. But many times, these infections trigger miscarriage randomly and don’t persist as an ongoing issue.
Advanced Maternal Age
The risks of miscarriage steadily rise as women get older, with more dramatic increases after age 35. Some key age-related factors behind this pattern include:
- Higher rates of chromosomal defects in eggs as women age, rising from 2-3% in a 20-year-old to 35% by age 40.
- Increased incidence of other medical conditions like diabetes, high blood pressure, thyroid disease.
- Declining number and quality of remaining eggs.
- Higher likelihood of uterine fibroids, polyps, and other structural issues.
By age 45, up to 80% of pregnancies will end in miscarriage. This age-related decline in fertility is natural, but also emphasizes why younger women have much higher success rates. Testing methods like preimplantation genetic screening (PGS) during IVF can help identify chromosomally normal embryos for older women to improve the odds.
Conclusion
Miscarriage is very common but also can be complex and frustrating to diagnose. Chromosomal issues are responsible for most first trimester losses, but thereafter, hormonal problems, chronic diseases, and uterine abnormalities become more influential as causes. Recurrent miscarriage involves a full workup, and may reveal treatable issues like thyroid disease, diabetes, or structural uterine defects. However, even with standard testing, about 50% of cases are unexplained. The bright side – after 1 or 2 losses, most couples still have good chances of a successful pregnancy in the future. Getting prenatal care early, controlling existing conditions optimally, and maintaining healthy lifestyle habits help stack the odds in your favor.