The earliest time in the pregnancy where the infant has at least a 50% chance of survival is called the "limit of viability". In countries with good health care, viability has been reduced to about 24 weeks. Rare survivors have been documented as early as 21 weeks, but this date is controversial because the pregnancy was measured from the date of conception rather than the date of her mother's last menstrual period. This makes gestation appear 2 weeks less than if calculated by the more common method. Risk of brain damage and developmental delay is significant at that early time. Even if the infant lives, there are ethical controversies over the care given to such infants. The limit of viability has also become a factor in the abortion debate.