Does urinary incontinence have fetal origins? Results from a nationwide twin study

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.

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).

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).

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.