Why does miscarriage occur? We explain the main causes of miscarriage.

A pregnancy is most vulnerable during Weeks 7 to 13. Repeated miscarriages can result from problems with: Implantation; genetics; immune disorders; physiology; hormones; toxin exposure; lifestyle; trauma; the mother’s age; and infections.

The fetus is abnormal in 70% of miscarriages.

Implantation problems mean the couple conceives but the fertilized egg cannot implant safely in the uterus for a full-term pregnancy.

A miscarriage that occurs in the first trimester of pregnancy (Day 1 to Week 12) is most likely to be caused by a genetic disorder with the fetus. For example, Turner’s syndrome is a genetic disorder that terminates 98% of affected pregnancies in the first trimester. Causes of miscarriage is important to understand so you can try to prevent another miscarriage in the future.

Late miscarriage in the second trimester (4 to 6 months) can happen from problems with the immune system or physiological problems.


The cause of miscarriage can be down to Immune system problems


The cause of miscarriage can be down to Physiological (mechanical) problems:

  1.  Uterine fibroid tumors Although they are benign (non-cancerous), fibroids can crowd out a pregnancy. Submucosal fibroids act like an IUD contraceptive to prevent the egg from implanting in the uterus.
  2.  Ectopic (tubal) pregnancy In 2% of pregnancies, the egg does not implant in the uterus, but stays in the fallopian tube, which ruptures when the embryo outgrows it.
  3.  Incompetent cervix In 1 out of every 100 pregnancies, the mother has a weak cervix due to a previous difficult delivery or miscarriage, or cervical surgery, D&C termination, birth defect, or exposure to the synthetic hormone DES (Diethylstilbestrol).

The cervix is weak and opens before the fetus can survive outside the mother’s body, usually in the second trimester (Weeks 13 to 27 of pregnancy) or third trimester (Weeks 28 to delivery). One-quarter of babies lost in the second trimester are due to incompetent cervix.

  1.  Placenta previa The placenta grows over the cervical opening and will tear in the second trimester.


The cause of miscarriage can be down to Hormonal problems

Progesterone deficiency is a hormonal problem where the pregnancy cannot be sustained past the tenth week without progesterone supplements.

During the latter half of a woman’s menstrual cycle (luteal), the ovary naturally secretes progesterone from the empty follicle in the ovary where the egg was released. Progesterone prepares the woman’s uterus for implantation of a fertilized egg. If the woman conceives, the empty follicle forms a corpus luteum (yellow body) that supports the pregnancy until the placenta is big enough to take over progesterone production.

If the egg (ovum) is fertilized, the corpus luteum (yellow body) in the ovary secretes progesterone to maintain the pregnancy until the placenta is large enough to take over production. Progesterone levels increase to 400 ng/ml of blood, and taper off during the last month of pregnancy to 200 ng/ml.

When you become pregnant, the corpus luteum supports the pregnancy for about the first 10 weeks. The placenta is the organ that attaches mother and child during pregnancy, and is expelled as afterbirth following the delivery. At about 8 to 10 weeks of pregnancy, the placenta in pregnant females is usually big enough to take over progesterone production from the ovaries and support the pregnancy after the tenth week. This is the critical moment for sustainability of the pregnancy and the danger time if progesterone production from the corpus luteum does not keep pace with the requirements of the growing fetus.

If the placenta does not produce sufficient progesterone to pick up the progesterone shortfall from the corpus luteum the placenta will become unstable and begin to breakdown. Spotting may occur and if not addressed with progesterone supplementation the pregnancy will usually miscarry. Natural hormone creams have been proven effective at supplementing the levels or progesterone in pregnant women.

By week 13 the placenta is sufficiently developed to support its own progesterone production and production continues to steadily increase until the end of the 8th month.

Pre-pregnancy normal daily progesterone production is around 20 milligrams per day during the luteal phase. During pregnancy, your progesterone production increases sharply to 400 milligrams by the third trimester (7 9 months). Estrogen also increases during pregnancy, but not as much as progesterone.

The progesterone level in the blood is a good indicator of the health of the placenta. Low progesterone levels are associated with amnionitis, intrauterine death, premature rupture of the membranes, premature labor, and placental abruption.


The cause of miscarriage can be down to Toxin exposure

Toxin exposure is likely to cause miscarriage. If you live or work near the flue gases of incinerators you are exposed to chlorinated hydrocarbons (CHC) that cause endometriosis, habitual abortion, and birth defects.

CHCs are stored in body fat. Hospital and food processing workers are likely to be exposed. Women who receive radiation exposure greater than 100 mSv can miscarry, and exposure greater than 10 mSv makes the child prone to cancer. Farm workers with chronic occupational exposure to herbicides and insecticides have difficulty reproducing because of low sperm counts, and have double the chance of birthing an infant missing a limb than the rest of the population.

If you are experiencing reproductive difficulty, find out if your farm uses these agricultural herbicides and insecticides:

Aldicarb; arsenic compounded with copper and lead; carbofuran; dinitrocresols; dinoterb; drazoxolon; endosulfan; endothal; fentin; mercuric chloride; mercury methyls, nitrobenzenes, oxydemeton-methyl, and thiofanox.


Other possible causes of miscarriage

A healthy lifestyle is crucial for maintaining your pregnancy. Women who are malnourished or diet excessively have difficulty maintaining a pregnancy. Smokers, drug users, women who drink more than two alcoholic beverages daily, and heavy coffee drinkers (more than 200 milligrams of caffeine per day) tend to miscarry more frequently.

Trauma rarely causes a miscarriage because the baby is well cushioned and insulated by the amniotic fluid and the mother’s body. Only 1,300 to 13,000 fetal deaths result per year in the U.S.A. from maternal injury in motor vehicle collisions. When trauma is sufficiently severe, it can cause premature rupture of the membranes (PROM) or abruptio placenta, where the placenta detaches from the wall of the uterus and severe bleeding occurs.

Extremes of age affect pregnancy outcome.

Girls under 15 have a tripled risk of neonatal death. Girls over 15 only have a 20% chance of miscarriage, providing they receive adequate prenatal care. A teenager is still growing, so the calcium diverted to her pregnancy softens her bones (osteoporosis).

Women who delay pregnancy past the age of 30 are most likely to have problems conceiving and carrying a pregnancy to full term. If you are younger than 35, you have a 15% chance of miscarriage. If you are 35 to 45 years old, you have a 20% to 35% chance of miscarriage.

If you are 45, you have a 50% chance of miscarriage. Women 46 and older have a 74.7% chance of miscarriage. Although you and your husband may be healthy, eggs (ova) and sperm deteriorate with age.

Infections such as malaria, syphilis, toxoplasmosis, mycoplasma, fifth disease (erythema infectiosum, commonly called €˜slapped cheek’), and chicken pox can cause miscarriage.


Who develops miscarriage?

Every healthy woman under the age of 35 has a 15% chance of miscarriage.

A chemical pregnancy occurs when a woman loses a newly implanted egg at the expected time of her period. Up to three-quarters of miscarriages are chemical pregnancies. The woman may not even know she was pregnant.

If you had one previous miscarriage, your chance of another miscarriage is not tremendously increased. There is a 25% chance that you will miscarry a second time. There is a 20% chance that you will be a habitual aborter with multiple miscarriages.

Diabetes, autoimmune diseases, and antiphospholipid syndrome (APS) place a pregnancy at additional risk.

Autoimmune disorders include rheumatoid arthritis, lupus, and scleroderma. The immune system defends the body against invaders, like viruses and bacteria. In autoimmune disorders, the immune system is overactive and attacks the body’s own tissues. Consequently, women with autoimmune disorders often have difficulty bringing a pregnancy to term.

Women with uterine fibroids, or who had a uterine fibroid embolization (UFE), or myomectomy to remove fibroids are at high risk for miscarriage.

Women with genetic disorders that affect their sex chromosomes have a higher incidence of miscarriage. For example, women suffering from Turner’s syndrome are prone to miscarriage. Type II Diabetic women and girls with juvenile rheumatoid arthritis are more likely to have Turner’s syndrome.


How often does a miscarriage happen?

Up to one-quarter of all confirmed pregnancies result in a miscarriage. Most miscarriages occur before Week 13 of pregnancy. Most countries do not include miscarriages in their pregnancy calculations because there is no way to count those that do not require in-patient hospitalization.
If this is your first pregnancy and you are one or two weeks pregnant, you have a 75% chance of miscarriage. You probably are unaware that you conceived because most home test kits detect a pregnancy no sooner than 14 days after ovulation.

If you are three to six weeks pregnant, you have a 10% chance of miscarriage.

If you are six to 12 weeks pregnant, you have a 5% chance of miscarriage.

Once your obstetrician can hear the fetal heartbeat, your pregnancy is even safer. You only have a 3% chance of a second trimester miscarriage.

In the third trimester, you only have a 1% chance of stillbirth.

If your first pregnancy miscarried, you have a 13% chance of recurrence. If you had at least one live birth and one miscarriage, you have a 10% chance of another spontaneous abortion (SAB). If you had multiple miscarriages and one live birth, you have a 13% chance of another miscarriage, providing you are younger than 35. However, if your first child was a live birth, followed by several SABs, your obstetrician must re-evaluate your risk.

If you had two live births and two miscarriages, you have a 40% chance of another SAB. If you had three pregnancies that all ended in miscarriage, then you have a 60% chance of another SAB and must go for testing.

If you had four consecutive pregnancies that all ended in miscarriage, then you have a 5% chance of delivering a live baby, at best perhaps less.

Ask your family doctor to refer you to a reproductive endocrinologist and then a fertility specialist.
Turner syndrome is responsible for 20% of all miscarriages that occur in the first trimester, and 98% of pregnancies affected by Turner’s syndrome end in miscarriage.

Many fetuses with hypogonadism have one or both kidneys missing (renal agenesis) and 10% to 33% of them will die in the uterus.

Infertility affects 15% of Australian couples. Infertility affects 12% of women aged 15 to 44 in the U.S.A., either because they cannot conceive, or they miscarry.

Mothers over 35 are more likely to miscarry.


Can I avoid a miscarriage?

Subfertile women who do fall pregnant may not be able to sustain the pregnancy past the tenth week. Progesterone is the hormone that supports a pregnancy. Before conceiving, a woman prone to miscarriage can try a low dose of natural progesterone cream from days 12 to 26 of her cycle until the pregnancy is confirmed.

If spotting occurs at week 6 or 7 of pregnancy, a high dose of 100 to 200 mg progesterone cream is applied twice or three times daily. Often, women use natural progesterone cream until the baby is full term (40 weeks of gestation).


Understand more on Miscarriage:

What is a miscarriage?

Signs & symptoms of miscarriage

What happens after miscarriage?

What is natural progesterone?

Progesterone treatment and side effects

The information in this article has been taken with permission from the official Lawley booklet on Understanding Miscarriage.