Birth injury refers to damage or injury to the child before, during, or just after the birthing process. "Birth trauma" refers specifically to mechanical damage sustained during delivery (such as nerve damage and broken bones).The term "birth injury" may be used in two different ways:

the ICD-10 uses "birth injury" and "birth trauma" interchangeably to refer to mechanical injuries sustained during delivery;
the legal community uses "birth injury" to refer to any damage or injury sustained during pregnancy, during delivery, or just after delivery, including injuries caused by trauma.Birth injuries must be distinguished from birth defects. "Birth defect" refers to damage that occurs while the fetus is in the womb, which may be caused by genetic mutations, infections, or exposure to toxins. There are more than 4,000 types of birth defects. Causes
Difficult labor (dystocia)
Difficult labor, also known as dystocia or obstructed labor, occurs when the child cannot easily pass through the birth canal. This can result in fetal distress or physical trauma to the child, especially broken clavicles and damage to the brachial plexus nerves. It can also deprive the child of oxygen as the umbilical cord is pinched, potentially causing brain damage or death.Difficult labor may occur because the baby is abnormally large (macrosomia), because the mothers pelvis or birth canal is small or deformed, or because the baby is in an abnormal presentation for the birth (such as breech or transverse presentation). External causes
Fetal malformations and birth injuries may occur as a result of exposure to environmental toxins such as mercury or lead.
Tetra-amelia syndrome (tetra- + amelia), also called autosomal recessive tetraamelia, is an extremely rare autosomal recessive congenital disorder characterized by the absence of all four limbs. Other areas of the body are also affected by malformations, such as the face, skull, reproductive organs, anus, lungs and pelvis. The disorder can be caused by recessive mutations in the WNT3 or RSPO2 genes. Presentation
Tetra-amelia syndrome is characterized by the complete absence of all four limbs. The syndrome causes severe malformations of various parts of the body, including the face and head, heart, nervous system, skeleton, and genitalia. In many cases, the lungs are underdeveloped, which makes breathing difficult or impossible. Because children with tetra-amelia syndrome have such serious medical problems, most are stillborn or die shortly after birth. Cause
RSPO2 and WNT3  genes
Researchers have found loss-of-function mutations in the WNT3 or the RSPO2 genes in people with tetra-amelia syndrome from several consanguineous families. These two gene encode proteins belonging to the WNT pathway which plays critical roles during development. The protein produced from the WNT3 and RSPO2 genes are involved in the formation of the limbs and other body systems during embryonic development. Mutations in the WNT3 or RSPO2 genes prevent cells from producing functional WNT3 and RSPO2 proteins, which disrupts normal limb formation and leads to the other serious birth defects associated with tetra-amelia syndrome. According to a 2018 study by Bruno Reversade, the loss of RSPO2, unlike WNT3, also prevents formation of the lungs causing a lethal syndrome of tetra-amelia.