In a 1989 study in Denmark, type I was found to comprise 71% of cases and type II 12% of cases, with other types comprising the other 17%. In a 2015 study in Sweden, type I was nearly six times more common than type III and nearly four times more common than type IV.Most people with OI receive it from a parent, but in many cases, it is a brand new (de novo or "sporadic") mutation in a family. Among a study of patients with survivable types of OI, OI type III is most often de novo (85%), followed by type IV (50%) and type I (34%). : Table 1 Some populations can have a higher incidence of OI than would be otherwise expected if they have a larger than average number of carriers of the recessive forms of the disease. : 20–21

History
The condition, or types of it, has had various other names over the years and in different nations; "osteogenesis imperfecta" has, however, been the most widely accepted name for the condition since the late 20th century. Among some of the most common alternatives are "fragilitas ossium"; "Ekman–Lobstein syndrome", and "Vrolik syndrome", both eponyms; and, the colloquialism, "brittle bone disease". Earliest recorded cases
OI has been identified in an ancient Egyptian infant mummified in around 1000 BC, originally dismissed by archaeologists as containing the remains of a monkey.
There are two subtypes of hydatidiform mole: complete hydatidiform mole, and partial hydatidiform mole. The four malignant tumours
Invasive mole
Choriocarcinoma
Placental site trophoblastic tumour
Epithelioid trophoblastic tumourAll five closely related tumours develop in the placenta. All five tumours arise from trophoblast cells that form the outer layer of the blastocyst in the early development of the fetus. In a normal pregnancy, trophoblasts aid the implantation of the fertilised egg into the uterine wall. But in GTD, they develop into tumour cells. Cause
Two main risk factors increase the likelihood for the development of GTD: 1) The woman being under 20 years of age, or over 35 years of age, and 2) previous GTD. Although molar pregnancies affect women of all ages, women under 16 and over 45 years of age have an increased risk of developing a molar pregnancy. Being from Asia/of Asian ethnicity is an important risk factor.Hydatidiform moles are abnormal conceptions with excessive placental development. Conception takes place, but placental tissue grows very fast, rather than supporting the growth of a fetus.Complete hydatidiform moles have no fetal tissue and no maternal DNA, as a result of a maternal ovum with no functional DNA. Most commonly, a single spermatozoon duplicates and fertilises an empty ovum. Less commonly, two separate spermatozoa fertilise an empty ovum (dispermic fertilisation). Partial hydatidiform moles have a fetus or fetal cells. They are triploid in origin, containing one set of maternal haploid genes and two sets of paternal haploid genes. They almost always occur following dispermic fertilisation of a normal ovum.