However, as shown in another report, in 11 of 42 pairs who were compared, “the future SIDS victim was more than 300 g lighter than his or her surviving sibling.” The conclusion was that the only items differentiating the SIDS infants from the control infants were a “lower mean weight and height at birth, the previous occurrence of cyanosis [bluish skin and mucous membranes caused by lack of oxygen in the blood] or pallor during sleep, and the recurrent profuse night sweats.”

In their report on 16 SIDS cases in England, a group of doctors stated: “SIDS usually occurs between 1 and 6 months of age with a peak at 2 to 4 months. . . . Other factors previously reported to be associated with SIDS are a maternal history of smoking during pregnancy, young maternal age at birth, unmarried status, large family size, [and] low socioeconomic status.” They add: “SIDS is also reported more frequently in male infants and is more prevalent during the autumn and winter months.” Yet, Bernard Knight cautions: “It must be emphasised that sudden infant death can​—and does—​strike at any family, irrespective of the position in the social hierarchy.”

Pathologists Try to Unravel the Mystery

When an infant dies without obvious cause, the coroner or medical examiner will usually call in a pathologist to examine the body and perform an autopsy. The reason for this is to try to pinpoint the exact cause of death and use this knowledge to prevent future cases. What have the pathologists found in many of these cases?

Over the years different trails have been followed. At one time SIDS was attributed to suffocation by pillows, bedclothing, and posture. That was rejected when it was proved that babies normally struggle out of any suffocation posture. And bedclothes are usually porous enough to allow for breathing. Then it was thought that bottle feeding and the use of cow’s milk was the cause. But breast-fed babies also died from SIDS. For a long time apnea, interrupted breathing, was blamed. Now that has been largely abandoned as a primary cause.

Some years ago some pathologists “truly believed that respiratory infection was the underlying cause of death . . . Though it is now [in 1983] generally thought that the infection is the trigger rather than the underlying cause, there is no doubt that some mild inflammatory condition of the air passages is implicated in a large proportion of SIDS.”​—Sudden Death in Infancy.

Professor Knight concludes that “it now seems obvious that there is no single cause of cot death” but that “there are several factors which come together in a given baby at a given time and cause death. We know some of the factors but not others.” Thus, the detective work continues as more clues are sought. Recently, however, a new discovery was made.

Hemoglobin Change​—Cause or Symptom?

This development was reported in The New England Journal of Medicine of April 30, 1987. It stated: “Prolonged elevation in the levels of fetal hemoglobin (hemoglobin F) in infants with SIDS could denote a compromised delivery of oxygen to sensitive tissue sites.”a The report indicated that after the birth of a baby, there is normal replacement of fetal hemoglobin with hemoglobin A produced by the baby’s body​—thus its own oxygen-carrying hemoglobin. In the victims of SIDS, a significant number of the victims still had a higher proportion of less effective fetal hemoglobin than was normal. So, what conclusion did the doctors draw?

“Our interpretation of this finding is that infants with SIDS are characterized by a marked delay in the switch from hemoglobin F to hemoglobin A​—a phenomenon that may reflect an underlying chronic condition.” Why does this happen? “The reason for the abnormal persistence of hemoglobin F is uncertain.”

Although they did not see this as a cause of SIDS, they did view it as a useful marker with which to pick out the babies that might be more subject to SIDS, “especially those beyond 50 weeks of post-conceptional age.”

The doctors who originated this study stated that “studies of SIDS suggest an association with low birth weight, prematurity, retarded growth development, and maternal smoking.”

This latter point is worthy of comment. Dr. Bernard Knight, of the University of Wales, Cardiff, wrote: “Quite a strong association of smoking with SIDS has been shown, though again it is difficult to know whether this is a direct link or merely an association with social factors.” Nevertheless, he does quote statistics that are revealing. In a survey of 50,000 births in the city of Cardiff, the rate of SIDS for mothers who have not smoked or who have stopped smoking was 1.18 per 1,000 live births. But for mothers who smoked more than 20 cigarettes a day, the figure jumped to 5.62 per 1,000 live births​—a fivefold increase!

Some mothers ask: “What about breast-feeding? Does that give greater protection against SIDS?” Dr. Bergman, prominent in the United States in the field of SIDS research, stated: “I happen to believe in breast feeding and I think it is better for a whole lot of reasons; but I don’t think that people who have lost crib death babies should have it suggested to them that their baby might still be alive if they had only breast fed.”

In view of the foregoing, is there anything parents can do to head off the threat of SIDS? Is it preventable?

[Footnotes]

Yet, even now, when so much more is known about the subject, Dr. Smialek admits: “Although SIDS is now widely accepted as a condition that parents have no power to predict or prevent, the occurrence of the simultaneous deaths of infant twins is a phenomenon that still evokes bewilderment and suspicion.”

But why should twins be more susceptible to SIDS? Pathologist Bernard Knight answers: “They are very often premature and are often under normal birth-weight. They more often need to spend the early part of their lives in special care units in maternity hospitals. . . . All these factors make them more vulnerable to sudden infant death.”