Causes of recurrent miscarriage

	Causes and risk factors	Examples
Epidemiological factor	Increase maternal age
	Increase paternal age
	Increase number of previous successive miscarriage
Genetic factor	Parental chromosomal abnormalities	Parent with balanced Robertsonian translocation
	Embryo chromosomal abnormalities	Embryo with imbalanced Robertsonian translocation
Anatomical factor	Congenital uterine malformation	Arcuate uteri, septate uteri
	Cervical weakness / incompetence
Maternal health condition	Anti-phospholipid syndrome
	Obesity
	Endocrine disorders	Thyroid disorder
		Diabetes mellitus
		Polycystic ovarian syndrome
	Thrombophilia
Infection	Bacterial vaginosis

Robertsonian translocation is a type of chromosomal rearrangement caused by fusion of 2 particular chromosomes. A person with Robertsonian translocation may have either a balanced translocation or an unbalanced translocation. When the translocation is balanced, the person with it is called Robertsonian translocation carrier. As a carrier, they are normal and healthy, and many of them never discover about their unusual chromosome rearrangement. Meanwhile, unbalanced translocation will lead to either a baby with congenital malformation or even a not viable one.

About 2 – 5 % of couples with recurrent miscarriage, one of the partner carries a balanced Robertsonian translocation (Robertsonian translocation carrier). There are 4 possible outcomes when 1 of the parent is a Robertsonian translocation carrier : 1) A normal baby. 2) The baby is a carrier. 3) A baby with congenital malformation. 4)Pregnancy loss, miscarriage.

Robertsonian translocation

Women with uncontrolled diabetes mellitus in 1st trimester are at risk of miscarriage and fetal malformation. However, a woman with well-controlled diabetes mellitus is not at risk of recurrent miscarriage.

Same with diabetes mellitus , thyroid dysfunction, if treated and well controlled, it is not a risk factor for recurrent miscarriage.

Meanwhile, increased risk of miscarriage in women with PCOS is said to be related to insulin resistance, hyperinsulinemia (high insulin in blood) and hyperandrogenemia (high androgen in blood).

Arcuate uterus increases the risk of 2nd trimester miscarriage and preterm labor ,while septate uterus is more likely to cause miscarriage in the 1st trimester. It is said that this is due to uterine distortion in these congenital uterine anomalies, which make the uterine unable to provide adequate support for the pregnancy.

Classification of congenital uterine anomalies