Back in the late 80's a new form of birth control was introduced. The Norplant system involved tiny match stick sized hormone implants which once inserted into the arm, prevented pregnancy.
Dr. Keith Brown, gynecologist, "We knew at that time overweight women had a greater chance of pregnancy with the Norplant."
If weight and failure rate were connected in the case of Norplant, does the same apply for other hormonal forms of birth control? The answer is yes.
Dr. Brown: "The pills the patch anything that has estrogen or progesterone in it as the contraceptive agent."
Dr. Brown says there are two theories as to why being overweight increases your risk of becoming pregnant while on birth control.
The first is oral contraceptives are fat soluble which means than can become trapped in fat--leaving fewer to circulate throughout the body. The second, The heavier the woman, the more liver enzymes which means drugs metabolize faster.
Either way being overweight increases the risk of contraception failure, and the more weight you have, that failure rate increases. With a Body Mass Index of 27-point three percent...that's a woman who is five-foot-five-one hundred 65-pounds, there's a sixty percent increase in failure rate..raise the B-M-I to 32--that risk increases to 70-percent.
Dr. Brown says for overweight women concerned about the failure rate of their birth control. There are other options like the I-U-D and the diaphram. Or he suggests, backing up the oral contraceptive or other birth control with a condom.
There are other things which can affect the effectiveness of hormonal birth control. Antibiotics, anti-convulsives, smoking and the drug Warfarin can all cause contraceptive failure.