The relationship between unplanned pregnancy and maternal body mass index 2009-2012

To analyse the relationship between unplanned pregnancy and maternal Body Mass Index (BMI).

A prospective case-control study of planned vs. unplanned pregnancies among women who delivered an infant weighing ≥ 500 g during the four years 2009-2012 in a large maternity hospital in Ireland. Maternal weight and height were measured at the first antenatal visit before calculation of BMI. Clinical and sociodemographic details were computerised. BMI was categorised according to the World Health Organization. The epidemiological associations were examined using logistic regression, adjusted for confounding variables.

Between 2009 and 2012, 34,377 women were included, 31.7% (n = 10,894) reported an unplanned pregnancy and 16.6% (n = 5647) were obese. The odds ratios of unplanned pregnancy were greater among obese women compared with those of normal BMI (unadjusted Odds Ratio (OR) 1.3; 95% Confidence Interval (CI) 1.3-1.4 p < 0.001). These ratios increased with increasing BMI (mild unadjusted OR 1.3; CI 1.2-1.4 p < 0.001; moderate unadjusted OR 1.4; CI 1.2-1.6 p < 0.001; severe obesity unadjusted OR 1.7; CI 1.4-2.0 p < 0.001). The higher rate of unplanned pregnancy among obese women was associated with a lower rate of contraception usage and a higher rate of contraceptive failure. Only 37.6% (n = 2112) of obese women took preconceptional folic acid to prevent neural tube defects compared with 46.1% (n = 8176) of women with a normal BMI (p < 0.001).

Higher rates of unplanned pregnancy among obese women compared with women with a normal BMI is associated with compromised prepregnancy care in this high-risk population.