Maternal weight is classified according to body mass index (BMI)A, with a BMI of 25 to 29.9 being classified as overweight and 30 or greater being defined as obese.

Overweight and obesity in pregnancy is associated with significantly increased risk of infant mortality (odds ratio 1.25 and 1.37, respectively),B even after adjusting for a range of potentially confounding factors including maternal age, parity,C smoking and education. This increased risk of infant mortality is due both to an increased risk of infant mortality in term births and an increased prevalence of preterm births in overweight or obese mothers. 1 Overall, one quarter (23%) of cases of late foetal loss, almost one third (30%) of stillbirths and a similar proportion (31%) of neonatal deaths were in obese women in the UK in 2005. 2

Some of the other possible health impacts of maternal obesity are listed in Table 2.

Table 2: Child health impacts of maternal obesity.

Effects on neonatal health Effects on childhood health Late effects on offspring’s health
Congenital anomalies[1]

Preterm or post-date deliveries

Neonatal intensive care admissions

Macrosomia (weight >4.5 kg)

Foetal growth restriction

Childhood asthma

Type 1 diabetes

Childhood obesity

Adult obesity

Cardiovascular disease

Type 2 diabetes


Source: Public Health England. 3

Maternal obesity also impacts on maternal mortality – one in five cases of maternal death is in obese women. Thromboembolism D is the most common direct cause of maternal death, with half of thromboembolic maternal deaths being in women who were overweight or obese. 4 Maternal obesity may also contribute to poor maternal health resulting from heart disease, pre-eclampsia E and gestational diabetes.F 5


  1. BMI is calculated as early as possible during the pregnancy by dividing the pregnant person’s weight (kilograms) by the square of their height (metres).
  2. An odds ratio represents the odds that an outcome (infant mortality) will occur given a particular exposure (maternal obesity), compared to the odds of the outcome (infant mortality) occurring in the absence of exposure (mother not overweight or obese),
  3. Parity refers to the number of pregnancies someone has carried to a viable gestational age (which is often equal to the number of times they have given birth).
  4. Thromboembolism refers to the obstruction of a blood vessel by a clot (thrombus) that either originated in that location or has been dislodged from another site in the body (embolism).
  5. Pre-eclampsia is a condition characterised by high blood pressure and protein in the mother’s urine and presents a risk that the mother may develop eclampsia, which involves fitting.
  6. Gestational diabetes is a type of diabetes (where the level of sugar in the blood is too high) that is first diagnosed during pregnancy, usually in the third trimester.


  1. S. Jahansson, E. Villamor, M. Altman, A.-K. Bonamy, F. Granath and S. Cnattingius, “Maternal overweight and obesity in early pregnancy and risk of infant mortality: a population based cohort study in Sweden,” BMJ, p. 349, 2014.
  2. “Maternal obesity and child outcomes,” Public Health England, 2016. [Online]. Available: [Accessed May 2016].
  3. “Maternal obesity and child outcomes,” Public Health England, 2016. [Online]. Available: [Accessed May 2016].
  4. “Maternal obesity and maternal health,” Public Health England, 2016. [Online]. Available: [Accessed May 2016].
  5. “,” Public Health England, 2015. [Online]. Available: [Accessed May 2016].