The Pregnancy Complications Of Maternal Obesity

New research to be published in BJOG: An International Journal of Obstetrics and Gynaecology points to a strong association between maternal obesity and adverse pregnancy outcomes.

Previous research has shown that maternal obesity is associated with pregnancy complications such as hypertensive disorders, gestational diabetes and maternal death; and fetal/neonatal complications such as stillbirth, birth defects, macrosomia (big baby syndrome) and shoulder dystocia.

The data for this research was from the Hyperglycaemia and Adverse Pregnancy Outcomes study (HAPO) which examined the associations of mild hyperglycaemia with pregnancy outcomes. There was strict selection and researchers looked at the records of 23,316 pregnant women from 15 centres in nine countries. All participants had their BMI measured and underwent a standard oral glucose tolerance test (OGTT) between 24 and 32 weeks gestation. Samples of their random plasma glucose (RPG) were taken at 34 - 37 weeks. Ethnicity was recorded and lifestyle data were also collated (eg. smoking levels, alcohol consumption, history of diabetes and hypertension etc) using standardised forms. After delivery (within 72 hours), the size of the babies was assessed using standard measures.

Researchers found that increased maternal obesity was strongly related to adverse pregnancy outcomes. For the mother, it includes a higher chance of having pre-eclampsia and delivery by caesarean section. For the newborn, it resulted in having a higher birthweight, increased fat deposits and neonatal hyperinsulinemia (excess levels of insulin in the blood). In this study, preterm delivery was less frequent with higher BMI, a finding that, as researchers note, is consistent with other large studies.

Researchers conclude that because obesity is rising in most societies, the results have important practical and health economic implications. In order to reduce adverse fetal and maternal pregnancy outcomes, prevention and optimum treatment of maternal obesity is needed.

Boyd Metzger, Professor of Metabolism & Nutrition at the Northwestern University Feinberg School of Medicine in Chicago, who led the study, said “This paper demonstrates clearly for the first time that both maternal obesity and maternal hyperglycaemia have important and independent effects on pregnancy outcomes. Previously, there has been debate over whether the effects of obesity are caused primarily by associated elevation of blood glucose and conversely some have argued that the effects of mild hyperglycaemia primarily reflect maternal obesity.

“The HAPO study data presented in this paper and in previous publications show that both factors strongly affect fetal size and fatness of infants at birth. Furthermore, both are strongly associated with preeclampsia, one of the commonest and most serious pregnancy complications.

“On a worldwide scale, the increasing prevalence of obesity is likely to strain health care resources, with increased rates of caesarean section and hypertension. Effects on the next generation due to the association of increased fetal adiposity with future diabetes and obesity may well compound the future effects of the epidemic of obesity.”

Professor Philip Steer, BJOG editor-in-chief said, “Across the developed world, we are experiencing an obesity epidemic. So much is being said about the world becoming fatter and unhealthier but if nothing constructive is being done now, then, this public health scare will become a harsh reality in the next generation.

“We have known about the pregnancy complications that result from a high BMI. This international study is further proof that something needs to be done urgently so that health outcomes for mother and baby are good.”


BJOG: An International Journal of Obstetrics and Gynaecology is owned by the Royal College of Obstetricians and Gynaecologists (RCOG) but is editorially independent and published monthly by Wiley-Blackwell. The journal features original, peer-reviewed, high-quality medical research in all areas of obstetrics and gynaecology worldwide. Please quote ‘BJOG’ or ‘BJOG: An International Journal of Obstetrics and Gynaecology’ when referring to the journal and include the website as a hidden link online.


“HAPO Study Cooperative Research Group. Hyperglycaemia and Adverse Pregnancy Outcome (HAPO) Study: associations with maternal body mass index.”
BJOG 2010; DOI: 10.1111/j.1471-0528.2009.02486.x.

Royal College of Obstetricians and Gynaecologists

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