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When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Most women experience menopause in their 50s. However, in 1994, an Italian woman gave birth to a baby boy when she was 61 years old.
Before a vaccine is licensed in the USA, the Food and Drug Administration (FDA) reviews it for safety and effectiveness. The CDC then reviews all studies again, as well as the American Academy of Pediatrics and the American Academy of Family Physicians. Every lot of vaccine is tested before administration to the public, and the FDA regularly inspects vaccine manufacturers' facilities.
About 3% of all pregnant women will give birth to twins, which is an increase in rate of nearly 60% since the early 1980s.