The most common causes of miscarriage

CHROMOSOMAL DEFECTS/ABNORMALITIES: Chromosomal defects/abnormalities are believed to account for up to 50% of all first trimester miscarriages. In many cases the pregnancy fails to develop past an empty gestational sac, these pregnancies are called 'blighted ovum' or 'anembryonic' pregnancies. Some experts believe that the risk of a blighted ovum pregnancy is higher in women with progesterone deficiency, but this is a subject of great debate and there is currently no evidence to support it.

PLACENTAL INSUFFICIENCIES/DEFECTS: Early in pregnancy the growing embryo is nourished by the corpeous luteum. Between weeks 10-12 the placenta begins to take over this role, and continues to do so until the baby is born. If the placenta is not attached properly to the uterine wall or has other defects, it will not be able to adequately nourish the baby which sometimes results in miscarriage.

BLOOD CLOTTING DISORDERS: Some women may have a disorder which causes their bodies to create blood clots in the placenta, thus making it impossible for the placenta to function correctly. This is a less common cause of miscarriage, but, unless diagnosed, can be responsible for recurrent miscarriages. The condition is treatable with medications designed to prevent the blood clots from forming.

UTERINE/CERVICAL PROBLEMS: Problems with the shape, size or structure of the uterus or cervix can result in miscarriage, often late in the first trimester or early in the second. Some examples of abnormalities that might cause miscarriage are: bicornuate uterus (where the uterus is heart shaped); septate uterus (where there is a division in the uterus separating it into two halves); incompetent cervix (where the cervix is unable to cope with the weight of the growing baby, resulting in very premature labour).

FERTILITY ISSUES: Studies have shown that women who undergo fertility treatment may be at higher risk of miscarriage. The reason for this is not clear, although some specific conditions, such as endometriosis, can contribute to miscarriage.

EXTRAUTERINE PREGNANCY: This is where the pregnancy grows outside of the uterus, usually in the fallopian tube but occasionally in the abdomen. These pregnancies always end in miscarriage, and can be life-threatening if not addressed early. Signs of an extrauterine pregnancy include dark red bleeding from the vagina, slow to rise hCG (pregnancy hormone) levels and strong pains in the abdomen which may be one-sided. The pregnancy must be removed or else it may rupture, this is usually done by laparoscopic surgery. In some cases the whole fallopian tube may need to be removed, but doctors will make every attempt to avoid this where possible.

MOLAR PREGNANCY: Also called a hydatidaform mole, a molar pregnancy is when the placental tissue grows abnormally resulting in a potentially cancerous growth. This is a rarer type of miscarriage, but requires immediate medical attention to remove the pregnancy, and on-going blood tests to ensure that the tissue doesn't continue to grow after the pregnancy is removed.

ABDOMINAL TRAUMA: A blow to the abdomen, such as those which occur during a car accident or fall, can cause the embryo/foetus to detach from the uterine wall, therefore resulting in inevitable miscarriage.

For support after miscarriage please visit:
Miscarriage Support NZ 
Miscarriage Matters NZ