From the first night, and whether it increases or in fact decreases the risks of SIDS depends on who sponsored the study you read.
http://www.babyreference.com/Cosleeping&SIDSFactSheet.htm
The crib industry (JPMA) provided a large forum for the Consumer Product Safety Commission (CPSC) to announce this report. Unfortunately, no comparative statistics are provided in their announcements, and even the statistics they report are admittedly anecdotal and irregular. While the report supposedly left out the adult bed deaths that were diagnosed as SIDS (versus accidents), the determination between suffocation and SIDS is often a judgment call. Suffocation in a crib is more often reported as SIDS, while suffocation in an adult bed is reported as "death by adult bed."
CO-SLEEPING AND SIDS
http://www.askdrsears.com/html/7/T071000.asp#T071006
http://pregnancy.about.com/b/2005/10/14/sids-pacifiers-co-sleeping.htm
The American Academy of Pediatricians (AAP) released a new policy statement on SIDS prevention. Some of the highlights of the policy statement were to have your baby sleep in a crib in your room, not in your bed, and to use a pacifier during sleep. This has lead to a firestorm of criticism from the medical and lay communities.
Dr. William Sears has issued a statement that says the AAP is ignoring much of the research done on SIDS and co-sleeping. He says that the majority of deaths that the AAP are talking about are not SIDS at all. Dr. Sears contends that the overwhelming majority of SIDS deaths occur in cribs.
La Leche League International (LLLI) also had something to say. Their statement says that the AAP ignored the work of Dr. James McKenna, famous infant sleep researcher. They are worried that the use of pacifiers, which the AAP calls a parent's decision, will cause a reduction in the amount of time a baby nurses, as has been shown in previous studies.
http://www.parenting.com/article/Baby/Health/Ask-Dr.-Sears-Co-Sleeping-a-SIDS-Danger
A. Don't worry; continue co-sleeping. Because I have thoroughly researched this common concern and written two books on the subject, The Baby Sleep Book and SIDS: A Parent's Guide to Understanding and Preventing Sudden Infant Death Syndrome, I feel that I can confidently advise you on this subject. In the SIDS book, you'll find more than 250 scientific references to support the information provided on sleep and breathing patterns, and safe sleeping arrangements.
http://www.babycenter.ca/baby/sleep/reducecotdeathexpert/
No hard and fast evidence proves that sleeping with your baby reduces the risk of cot death or, to use the medical term, Sudden Infant Death Syndrome (SIDS). Some research suggests that co-sleeping may reduce the risk of cot death for the following reasons:
1. Small babies cannot control their bodily temperature easily. Co-sleeping allows mother and baby to act as a thermostatic unit -- when the baby heats up, the mother cools down, bringing her baby's temperature down with hers.
2. Many small babies have breathing pauses (apneoa). Co-sleeping allows you to be aware of these pauses, even in your sleep. You move or make sounds that bring your baby to a brief arousal so that he can tune into your breathing and join in again at the same pace, without waking fully.
However, studies show that the risk of cot death increases when one or both co-sleeping parents is drunk, has taken drugs, is a smoker or is obese. One study published in The Lancet in 2004 also suggests that the risk of cot death increases if parents sleep with a baby who is younger than eight weeks old (regardless of whether they have been drinking, smoking or taking drugs).