Introduction and hypothesis: The aim of this study is to evaluate the effect of birth weight and being born small for gestational age (SGA) on urinary incontinence (UI) among premenopausal women.
Methods: In 2005, a total of 14,094 female twins born 1959-1985 who had been included in the Swedish Twin Registry participated in a survey on common exposures and complex diseases, including urinary incontinence. Information regarding birth weight and gestational age was obtained from the Medical Birth Register (for twins born 1973-1985) and from the medical archives (for twins born 1959-1972). A logistic regression model based on generalized estimating equations was used to estimate odds ratios (ORs) with 95 % confidence intervals (CIs).
Results: In both crude and adjusted analysis, birth weight and SGA had no effect on UI. An interaction between low birth weight (<2,500 g) and body mass index (BMI) later in life was found for overall and stress UI. Compared with women who were not overweight and had a birth weight above 2,500 g, overweight women (BMI ≥ 25) who had a normal birth weight had a 35 % higher odds of incontinence , while overweight women who had a low birth weight had an approximately 85 % higher odds of UI (OR = 1.84, 95 % CI 1.39-2.45 for overall UI; OR = 1.83, 95 % CI 1.35-2.48 for stress UI).
Conclusions: Birth weight and SGA had no direct effect on urinary incontinence; however, low birth weight in combination with an elevated adult BMI may contribute to the risk of urinary incontinence later in life.