Large congenital nevi form in the womb very early in development, within the first twelve weeks of pregnancy. They are caused by a defect during embryologic development. There is no known method of prevention. They appear in either sex, in all races, and on any areas of the skin.
I recommend that you have a carbon monoxide detector within 15 feet of each bedroom door, 10 feet is even better if you can afford more detectors. If two bedroom doors are 30 feet apart or less, then place one in the middle. If however they are more than 30 feet apart you will need more than one detector.
October 29, 2012. Carbon Monoxide Detectors: Guaranteed to Fail in 7 Years. To help prevent illness and death, some states require carbon monoxide alarms to be installed in various parts of your home. Kidde is one of the large, recognized brands of smoke alarms and other fire prevention products. Certain of their carbon monoxide detectors, however, come with conflicting promises and warnings.