Causes of miscarriage

By (embryologist) and (fertility counselor).
Last Update: 04/16/2014

Many people wonder about what the main causes of a miscarriage are. In order to understand exactly these causes, it is necessary to know and understand what a miscarriage is.

It is considered as a miscarriage the pregnancy loss before the fetus is in conditions of surviving and staying alive outside the mother's uterus. Between 8% and 15% of the pregnancies end up in this way, although it is thought to be an important number of unnoticed miscarriages. The causes for a miscarriage are not completely clear. However, most of them are produced because of a pregnancy that was not being developed normally and, so, there is nothing that either the woman or the doctor can do to avoid it. Among the most frequent causes we can find:

Genetic causes

The chromosomal abnormalities in the fetus are very frequent, which makes than over 50% of miscarriages that occur during the first trimester of pregnancy start out in the chromosomal abnormalities of the fetus.

The chromosomes are the tiny cell structures where all our genes are. Each person has 23 pairs of chromosomes, for a total of 46 chromosomes. A chromosome from each pair comes from the father and the other from the mother.
Most of the chromosomal abnormalities are because of a defective sperm or a defective egg which has too many or too few chromosomes, which leads to a miscarriage.

The chromosomal abnormalities are more frequent as the parents are older, and so does the risk of a miscarriage. These abnormalities are mainly trisomies and, in few cases, triploid. These alterations tend to cause blighted ovum and very early miscarriages, before week eight. Most of these early miscarriages are caused by genetic reasons. Usually, if a woman suffers a second miscarriage in a row, her genetic analysis or karyotype is related to the first miscarriage.

Causes of miscarrige

Are the most frequent in repeated miscarriage. Many times it is because of an incompatibility between the mother and the embryo due to immunological similarities. It is also possible that the mother produces antibodies against her own body, which can cause thrombosis and occlusions of placental vessels, leading to miscarriages. These kind of factors tend to cause late fetal deaths.


Anatomical causes

Being the most frequent: an irregular shape of the uterus and a weak cervix. The fist has to do with problems that come back from the birth of the mother. The uterus has malformation called uterus didelphys, which is basically a double uterus with two separate cervices. The second cause occurs when the cervix start to open as the uterus becomes heavier and, consequently, it is unable to keep the embryo. A weak cervix is the most frequent cause and its diagnose is very easy; with an ultrasound the doctor can check the cervix state and, consequently, can provide some preventive measures.


Physiological and endocrine causes

They are related to the so-called progesterone deficiency or a luteal phase deficiency. Until the first eight or nine weeks of pregnancy, keeping up the pregnancy depends very much on the adequate production of progesterone in the corpus luteum. If there is a drop off in production of this hormone, there can be problems with the embryo implantation. Within this group of causes, a poorly controlled diabetes, caused by a alteration of thyroid function, could be included. Another caused included in this group is the polycystic ovary syndrome.



Some infections caused by cytomegalovirus, chlamydia, mycoplasma, etc., or specific infections such as syphilis or listeriosis might lead to a miscarriage. The use of an intrauterine device as a contraceptive method can also produce uterine infections that are hard to control.

Apart from these factors, the risk of a miscarriage is also influenced by the mother's lifestyle. Smoking, alcohol-drinking or drug-user mothers have a high risk of suffering a miscarriage. Being overweighted has also a negative influence.

Therefore, it is regarded as something very important for the woman to take good care of herself from the very first moment that she decides to get pregnant. If she has a healthy lifestyle, many of these problems would be solved. Since her partner gives the other half of the genetic material, it is also important for him to keep a healthy lifestyle.


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 Neus Ferrando Gilabert
Neus Ferrando Gilabert
B.Sc., M.Sc.
Bachelor's Degree in Biology from the University of Valencia (UV). Postgraduate Course in Biotechnology of Human Assisted Reproduction from the Miguel Hernández University of Elche (UMH). Experience managing Embryology and Andrology Labs at Centro Médico Manzanera (Logroño, Spain). More information about Neus Ferrando Gilabert
Adapted into english by:
 Sandra Fernández
Sandra Fernández
B.A., M.A.
Fertility Counselor
Bachelor of Arts in Translation and Interpreting (English, Spanish, Catalan, German) from the University of Valencia (UV) and Heriot-Watt University, Riccarton Campus (Edinburgh, UK). Postgraduate Course in Legal Translation from the University of Valencia. Specialist in Medical Translation, with several years of experience in the field of Assisted Reproduction. More information about Sandra Fernández

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