The reason why most miscarriages happen at 7 weeks is because of chromosomal abnormalities in the developing fetus.
Chromosomal abnormalities in the developing fetus prevent the fetus from developing properly and the abnormalities can lead to the inability of the fetus to survive which leads to the miscarriage.
Other factors that can cause miscarriages include infections, smoking or drug use and even uterine abnormalities.
The development of the antibodies against H-Y antigens is also thought to be a contributing factor to the increased risk of miscarriage in any subsequent pregnancies, especially if the fetus is also a male fetus.
A significant portion of early miscarriages are a result of chromosomal problems in the fetus.
And older mothers are also slightly at higher risk for miscarriages.
And even some genetic predispositions can also increase the woman's risk of miscarriage.
Other factors that can result in miscarriage include stress, drug use, smoking and excessive alcohol consumption.