Chromosomal abnormalities – The units in the cell nucleus holding the hereditary information, the chromosomes are not normal. Studies show more than 50 percent of all first trimester miscarriages are caused by these abnormal chromosomes. The abnormalities may be inherited from either parent. Most are dues to a mistake in the number of genes (pieces of hereditary information) in the egg or sperm. Genetic studies of you or your partner might be suggested if you have had two or more pregnancy losses. If abnormal genes run in the family, these studies may also be considered.
Defective implantation – The fertilized egg is in the uterus but is unable to attach to the wall of the uterus. The pregnancy cannot continue normally.
Placental problems – The placenta is the life-support system for the baby from the mother. Problems in the growth or functioning of the placenta may prevent the fetus from getting enough nourishment. Placental problems can also include involvement with the umbilical cord.
Hormonal imbalance – If there is not enough progesterone in the uterus, the lining of the uterus is not able to care for the fertilized egg. (Fertility drugs can sometimes add to hormonal imbalance.) This low level can only be diagnosed before pregnancy.
Uterine disorder – Malformation of the uterus may be something which you are born with or the result of disease or chemical exposure.
Infection – Examples of disease risky to the fetus are syphilis and herpes simplex. Both are sexually transmitted infections. CMV (cytomegalovirus) is another disease that puts a pregnancy at risk.
Incompetent cervix – In some women, the cervix is very weak. This may be something you were born with or the result of obstetrical or surgical injury. Miscarriage usually occurs later in the pregnancy as the baby becomes heavier. The cervix does not stay closed long enough to complete the pregnancy.
Sperm problems – Miscarriage might sometimes occur as a result of a very high or very low sperm count. Poor quality of sperm can also cause loss. Decreased DNA in sperm can end a pregnancy. Certain diseases in the father, such as diabetes, can contribute to possible miscarriage. Exposure to toxic substances can also be linked to miscarriage and birth defects.
ABO incompatibility – The different blood types of the parents can cause miscarriage. This type of miscarriage usually occurs late in pregnancy.
CMV (Cytolomegalovirus) – CMV is spread by frequent contact with the urine or saliva of another who carries the virus. Some bacterial infections causing miscarriage are pneumonia, urinary tract infections, bowel infections and uterine infections. Viral infections able to cause a miscarriage are hepatitis, polio, encephalitis, chickenpox, toxoplasmosis and measles.
Environmental causes – Pollutants, cigarette smoking, poor eating habits and drug abuse have been linked to higher rates of miscarriage. The frequency of miscarriage is doubled in women who are moderate to heavy drinkers.
Age factors – There appears to be an increased risk of miscarriage after the age of 35 as well as before the age of 18.