The exact cause of<unk>  is unknown. Although studies have identified risk factors for<unk> , such as putting<unk> s to bed on their bellies, there has been little understanding of the<unk> 's biological process or its potential causes.<unk> s from<unk>  are unlikely to be due to a single cause, but rather to multiple risk factors. The frequency of<unk>  does appear to be influenced by social, economic, or cultural factors, such as maternal education, race or ethnicity, or poverty.<unk>  is believed to occur when an<unk>  with an underlying biological vulnerability, who is at a critical development age, is exposed to an external trigger. The following risk factors generally contribute either to the underlying biological vulnerability or represent an external trigger: Tobacco smoke<unk>  rates are higher in babies of mothers who smoke during pregnancy. Between no smoking and smoking 1 cigarette a day, on average, the risk doubles. About 22% of<unk>  in the United States is related to maternal smoking.<unk>  correlates with levels of nicotine and its derivatives in the baby. Nicotine and derivatives cause alterations in neurodevelopment. Sleeping Placing an<unk>  to sleep while lying on the belly or side rather than on the back increases the risk for<unk> . This increased risk is greatest at two to three months of age. Elevated or reduced room temperature also increases the risk, as does excessive bedding, clothing, soft sleep surfaces, and stuffed animals in the bed. Bumper pads may increase the risk of<unk>  due to the risk of suffocation. They are not recommended for children under one year of age, as this risk of suffocation greatly outweighs the risk of head bumping or limbs getting stuck in the bars of the crib. Sharing a bed with parents or siblings increases the risk for<unk> . This risk is greatest in the first three months of life, when the mattress is soft, when one or more persons share the<unk> 's bed, especially when the bed partners are using drugs or alcohol or are smoking. The risk remains, however, even in parents who do not smoke or use drugs. The American Academy of Pediatrics thus recommends "room-sharing without bed-sharing", stating that such an arrangement can decrease the risk of<unk>  by up to 50%. Furthermore, the Academy has recommended against devices marketed to make bed-sharing "safe", such as "in-bed co-sleepers". Room sharing as opposed to solitary sleeping is known to decrease the risk of<unk> . Breastfeeding Breastfeeding is associated with a lower risk of<unk> . It is not clear if co-sleeping among mothers who breastfeed without any other risk factors increases<unk>  risk. Pregnancy and<unk>  factors<unk>  rates decrease with increasing maternal age, with teenage mothers at greatest risk. Delayed or inadequate prenatal care also increases risk. Low birth weight is a significant risk factor. In the United States from 1995 to 1998, the<unk><unk>  rate for<unk> s weighing 1000–1499 g was 2.89/1000, while for a birth weight of 3500–3999 g, it was only 0.51/1000. Premature birth increases the risk of<unk><unk>  roughly fourfold. From 1995 to 1998, the U.S.<unk>  rate for births at 37–39 weeks of gestation was 0.73/1000, while the<unk>  rate for births at 28–31 weeks of gestation was 2.39/1000. Anemia has also been linked to<unk>  (however, per item 6 in the list of epidemiologic characteristics below, extent of anemia cannot be evaluated at autopsy because an<unk> 's total hemoglobin can only be measured during life).<unk>  incidence rises from zero at birth, is highest from two to four months of age, and declines toward zero after the<unk> 's first year. Genetics Genetics plays a role, as<unk>  is more prevalent in males. There is a consistent 50% male excess in<unk>  per 1000 live births of each sex. Given a 5% male excess birth rate, there appears to be 3.15 male<unk>  cases per 2 female cases, for a male fraction of 0.61. This value of 61% in the US is an average of 57% black male<unk> , 62.2% white male<unk>  and 59.4% for all other races combined. Note that when multiracial parentage is involved,<unk>  race is arbitrarily assigned to one category or the other; most often it is chosen by the mother. The X-linkage hypothesis for<unk>  and the male excess in<unk>  mortality have shown that the 50% male excess might be related to a dominant X-linked allele, occurring with a frequency of that is protective against transient cerebral anoxia. An unprotected male would occur with a frequency of and an unprotected female would occur with a frequency of . About 10 to 20% of<unk>  cases are believed to be due to channelopathies, which are inherited defects in the ion channels which play an important role in the contraction of the heart. Genetic evidence published in November 2020 concerning the case of Kathleen Folbigg, who is in prison over the<unk>  of four of her children, showed that at least two of the children had genetic mutations in the CALM2 gene that predisposed them to heart complications. Alcohol Drinking of alcohol by parents is linked to<unk> . One study found a positive correlation between the two during New Years celebrations and weekends. Another found that alcohol use disorder was linked to a more than doubling of risk. Other<unk>  has been linked to cold<unk> er, with this association believed to be due to over-bundling and thus, overheating. Premature babies are at four times the risk of<unk> , possibly related to an underdeveloped ability to automatically control the cardiovascular system. A 1998 report found that antimony- and phosphorus-containing compounds used as fire retardants in PVC and other cot mattress materials are not a cause of<unk> . The report also states that toxic gas cannot be generated from antimony in mattresses and that babies suffered<unk>  on mattresses that did not contain the compound. It has been suggested that some cases of<unk>  may be related to Staphylococcus aureus and Escherichia coli infections.
Sudden infant death syndrome
Genetic disorder
Shaken baby syndrome
Infection
Blue baby syndrome
Child abuse
Neonatal meningitis
Infant respiratory distress syndrome