Definition of Acclimatization to altitude

Acclimatization to altitude: The main cause of altitude sickness is going too high too fast. Given time, the body can adapt to the decrease in oxygen concentration at a specific altitude, process known as acclimatization.
To acclimatize, a number of changes take place in the body occur to allow it to operate with decreased oxygen:

The depth of respiration increases;
The pressure in the pulmonary arteries increases, forcing blood into portions of the lung which are normally not used at sea level;
We make more red blood cells to carry oxygen;
We make more of a specific substance (called 2,4-DPG)that facilitates the release of oxygen from hemoglobin to the body tissues.
Acclimatization generally takes 1 to 3 days at a given altitude. For example, if a person hikes to 10,000 feet (3,048 meters) and spends several days at that altitude, their body acclimatizes to 10,000 feet (3,048 meters). If the person then climbs to 12,000 feet (3,658 meters), the body needs to acclimatize once again and it takes another 1 to 3 days.

Definition of Abstinence, periodic

Abstinence, periodic: Also known as fertility awareness, natural family planning, and the rhythm method, this approach entails not having sexual intercourse on the days of a woman's menstrual cycle when she could become pregnant or using a barrier method (such as a condom, the diaphragm or a cervical cap) for birth control on those days.
Because a sperm may live in the female's reproductive tract for up to 7 days and the egg remains fertile for about 24 hours, a woman can get pregnant within a substantial window of time -- from 7 days before ovulation to 3 days after. Methods to approximate when a woman is fertile are usually based on the menstrual cycle, changes in cervical mucus, or changes in body temperature.