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. Author manuscript; available in PMC: 2014 Jun 1.
Published in final edited form as: Fertil Steril. 2013 Mar 18;99(7):1958–1964. doi: 10.1016/j.fertnstert.2013.02.040

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Association between age and fecundability, fitted by restricted cubic splines. Reference level for FR is 20 years. All curves used 3 knots located at 25, 30, and 35 years, except for the male curves, which have an additional knot at age 40. In the first two panels, the unadjusted curve controls for cycle number only, and the adjusted curve controls for cycle number, partner’s age, vigorous physical activity, BMI, vocational training, alcohol intake, current smoking, pack-years of smoking (ever smokers), partner smoking, partner BMI, cycle length, cycle regularity, parity, intercourse frequency, last method of contraception, and methods used to time intercourse. In the third panel, both curves control for cycle number, female age, vigorous physical activity, BMI, vocational training, alcohol intake, current smoking, pack-years of smoking (ever smokers), partner smoking, partner BMI, cycle length, cycle regularity, parity, intercourse frequency, last method of contraception, and methods used to time intercourse.