Obesity rates have reached epidemic proportions globally and have been shown to adversely influence many clinical markers of health However, the data are sparse with regards to the effect maternal obesity may have on fetal and neonatal outcomes. A recent report in Lancet, by Di Cesare et al, showed that the number of women aged 18 years and older with a BMI of > 35 (obesity class II and III) doubled from approximately 50 million to 100 million worldwide between 2000 and 2010– making it clear that obesity should be considered a major health concern in women of child bearing age.
Previous studies have shown that maternal obesity (defined as a BMI of > 30) increases the risk of congenital malformations ranging from heart defects to malformations of the nervous, genital and digestive systems as well as limb defects. It is unknown, however, if there are similar risks in offspring of women whose BMI defines them as ‘overweight’ (BMI 25 to <30) and whether risks increase with increasing rise in BMI. To gain further insight into this gap, a population based cohort study was conducted using data from the Nationwide Swedish registries from 1,243,957 live born singleton infants from 2001-2014 in Sweden and results published in May 2017 in BMJ (British Medical Journal).
Highlighted results from this study include the following:
- Risk for any major congenital malformation increased with maternal overweight and severity of obesity
- Overall risk of any major congenital malformation was higher in male infants than females with higher risk increasing with maternal severity of obesity in both male and female offspring
- The greatest organ specific risk ratios related to increased maternal obesity were found in nervous system malformations
- The most prevalent subtype of organ specific malformations were found in congenital heart defects. These increased with maternal overweight and rose with increased weight in a dose-response pattern
Diabetes and dysglycemic states are common complications of pregnancy and may increase risk of congenital malformations. However, the data from this study found that there was essentially an unchanged risk of congenital malformations after exclusion of diabetic mothers. This further supports conclusions from prior research.  The authors hypothesize this may be due to the role of other metabolic dysfunctions associated with high BMIs including insulin resistance, hyperlipidemia and inflammation. Further research is needed to elucidate mechanisms for these results.
Why is this Clinically Relevant?
- Preconception education concerning healthy maternal BMIs and fetal and neonatal outcomes should be given to all women of child bearing ages who are considering a future pregnancy
- Preconception healthy lifestyle programs should be offered for all overweight and obese women of child bearing age when considering pregnancy
- It is important to screen patients prior to conception for elevated BMI associated with congenital malformations
 Di Cesare M, et al. NCD Risk Factor Collaboration. Trends in adult body-mass index in 200 countries from 1975 to 2014; a pooled analysis of 1698 population-based measurement studies with 19.2 million participants. Lancet. 2016; 387:1377-96.
 Persson M, et al. Risk of major congenital malformations in relation to maternal overweight and obesity severity: cohort study of 1.2 million singletons. BMJ. 2017; 357:j2563.
 Waller DK, et al. National Birth Defects Prevention Study. Prepregnancy obesity as a risk factor for structural birth defects. Arch Pediatr Adolesc Med. 2007; 161:745-50.