Obesity is on the rise in the Canadian population and has been linked to increased birth difficulties and perinatal death. This systematic review reveals that maternal obesity is also associated with an increased risk of various congenital anomalies, such as spina bifida. Since several of these conditions are also related to poor nutrition, obese women who want to become pregnant, should be made aware of the risks and offered counselling on weight loss strategies and improved nutrition to avoid a higher risk of congenital anomalies. Background: Public health officials have reported on the increasing prevalence of obesity in Canada. There are significant health implications of prepregnancy obesity for the child such as increased birth difficulties, perinatal death, and the development of congenital abnormalities. The authors conducted a systematic review and meta-analysis of observational studies to further examine the relationship between maternal overweight (i.e., body mass index (BMI) between 25 and 30) and obesity (i.e., BMI > 30) before becoming pregnant and the risk of congenital abnormalities (e.g., neural tube defects, cardiovascular anomalies, and orofacial clefts) in their children.

Methods: Data extraction was completed by four reviewers (each study independently reviewed by two individuals) using a standardized, piloted data extraction form. There were no discrepancies between reviewers in deciding which articles to include and the information extracted. Meta-analysis was conducted according to published guidelines and adjusted for bias (i.e., negative findings not published). A sensitivity analysis was performed to examine the effects of varying methodological quality and inclusion criteria.

Findings: The systematic review included 39 articles, of which 18 were included in the meta-analysis. Mothers who were obese before becoming pregnant had almost twice the odds of having a child with a neural tube defect compared with mothers of recommended BMI and overweight. Furthermore, o women, but not overweight women, were also much more likely to have pregnancy complicated by spina bifida, heart septal anomalies, and orofacial clefts. Both obese and overweight women had higher odds of having a pregnancy affected by a cardiovascular anomaly. The sensitivity analyses did not result in changes to the findings.

Conclusions: In general, prepregnancy obesity, but not maternal overweight, was strongly associated with an increased risk of most congenital abnormalities examined in the study. The authors suggest mechanisms for the observed association are: (i) undiagnosed diabetes, (ii) difficulty in ultrasound screening in obese women that results in fewer terminated pregnancies affected by congenital anomalies, and perhaps most importantly, (iii) nutritional deficiencies such as reduced folate intake. Awareness should be raised on the dangers to the unborn foetus associated with prepregnancy obesity, and obese women seeking to become pregnant should be counselled on weight loss strategies and improved nutrition to reduce the identified risk of congenital abnormalities.


Stothard KJ, Tennant P, Rankin J. Maternal overweight and obesity and the risk of congenital abnormalities: A systematic review and meta-analysis. JAMA, 2009; 301(6): 636-650.