INTRODUCTION
Obesity is a significant public health concern. There is a rising trend for increased body mass index (BMI) across all age groups with obesity rates tripling over the past 40 years 1. The World Health Organization (WHO) reported that 39% of adults aged 18 years and over were overweight in 2016, and 13% were obese with obesity being a major risk factor for non-communicable diseases including type 2 diabetes and cardiovascular diseases 2. A global systematic analysis found that women of reproductive age demonstrate a particularly steep increase in obesity prevalence 3, with 38.9 million pregnant women estimated to be overweight and 14.6 million estimated to be obese, in 2014 4. In Australia, nearly half of women who gave birth were overweight or obese in 2017 5. A similar trend in overweight and obesity prevalence has also been seen in men of reproductive age3.
There is consistent evidence that maternal preconception BMI affects infant birthweight, such that maternal overweight or obesity increases the likelihood for an infant being born large for gestational age (LGA) (OR=1.45; 95%CI=[1.29, 1.63] and OR=1.88; 95%CI=[1.67, 2.11], respectively) or macrosomic (OR=1.70; 95%CI=[1.55, 1.87] and OR=2.92; 95%CI=[2.67, 3.20], respectively) 6. In comparison the risk of delivering a small for gestational age (SGA) baby are increased in underweight mothers (OR = 1.67; 95% CI = [1.49-1.87]); but decreased with overweight (OR=0.71; 95%CI=[0.66, 0.76]) or obese mothers (OR=0.88; 95%CI=[0.78, 0.99]) 6. Increased maternal BMI also influences child overweight and obesity risks up to 14 years of age7 and increases future risk for obesity and cardio-metabolic diseases later life for both mother and child8. Problematically, the potential impact of paternal BMI is rarely considered in these studies, despite a small body of evidence suggesting that paternal preconception overweight and obesity may also contribute to infant birthweight including the delivery of an SGA or LGA infant 9, 10. Thus the involvement of paternal overweight and obesity on infant birthweight demonstrates a role for the father’s preconception health in programing fetal outcomes11.
It is evident that maternal preconception BMI affects infant birthweight, however the influence of paternal preconception BMI is less studied. Further it is unclear whether there is an additional effect on infant birthweight if both parents are overweight or obese. We hypothesise that the combination of both maternal and paternal preconception overweight/obesity has a larger contribution to infant birthweight than their independent parental effects. The objective of this study is to assess the independent and combined effects of maternal and paternal preconception overweight and obesity on infant birthweight utilising an assisted reproductive technologies (ART) cohort where preconception parental BMI is routinely collected.