Early pregnancy obesity is significantly associated with fetal and infant death, independent of congenital anomalies and maternal pregestational diabetes, according to the results of a cohort study reported online April 5 in Human Reproduction.
“We are the first investigators to examine the continuous relationship between BMI [body mass index] and foetal and infant deaths,” said lead study author Peter W.G. Tennant, research assistant at Newcastle University, Newcastle upon Tyne, United Kingdom, in a news release. “Our study suggests the optimal BMI, for the child at least, is somewhere around 23, but further research is needed to confirm this.”
The investigators linked data on singleton pregnancies delivered during 2003 to 2005 at 5 hospitals with data from 3 regional registers: the Northern Perinatal Mortality Survey, the Northern Diabetes in Pregnancy Survey, and the Northern Congenital Abnormality Survey. Spontaneous fetal death was defined as death at 20 weeks’ gestation or more, infant death as death up to age 1 year, underweight as a BMI of less than 18.5 kg/m2, overweight as a BMI of 25 to 29.9 kg/m2, obese as a BMI of 30 kg/m2 or more, and recommended BMI as 18.5 to 24.9 kg/m2.
Crude and adjusted odds ratios (ORs) of spontaneous fetal death and infant death among underweight, overweight, and obese women vs women of recommended BMI were determined with use of logistic regression models.
Risks for fetal death as well as infant death were significantly increased in obese women (adjusted OR, 2.32; 95% confidence interval [CI], 1.64 – 3.28; P < .001 and adjusted OR, 1.97; 95% CI, 1.13 – 3.45; P = .02, respectively). Continuous analyses demonstrated a V-shaped association between BMI and the risks for fetal and infant death. Risk was at the minimum at a BMI of 23 kg/m2, and this risk significantly increased thereafter both for fetal death (adjusted OR per unit, 1.07; 95% CI, 1.05 – 1.10; P < .001) and infant death (adjusted OR per unit, 1.06; 95% CI, 1.02 – 1.10; P = .007).
As categories, no significant excess risks were demonstrated for either maternal underweight or maternal overweight. Among obese women, there was no specific cause of death explaining the increased odds of fetal and infant death, except for higher rates of preeclampsia among stillbirths.
“There are likely to be a number of reasons why obesity is associated with foetal and infant death and we don’t yet know the full story,” said coauthor Judith Rankin, professor of maternal and perinatal epidemiology at Newcastle University and academic director at the Regional Maternity Survey Office (RMSO). For example, there is an increased risk of high blood pressure or diabetes developing during pregnancy. Understanding the risks associated with obesity is helpful for healthcare professionals caring for pregnant women, so that additional monitoring can be provided as necessary.”
Limitations of this study include reliance on self-report for weight and height information and inability to determine if lifestyle factors such as diet, exercise, alcohol consumption, and caffeine consumption affected pregnancy risks.
“It’s important to remember that most women in the UK will deliver a healthy live baby, regardless of their weight at the start of pregnancy,” said senior author Ruth Bell, clinical lecturer in the Institute of Health and Society at Newcastle University and RMSO associate director. “What’s key is that women should be helped to achieve a healthy weight before they become pregnant or after the baby is born. Our research shows that this will give the baby the best possible start in life. Women should not try to lose weight during pregnancy, but should ensure they eat a balanced healthy diet.”
The Primary Care Trusts in the North of England and the Healthcare Quality Improvement Partnership supported this study. The study authors have received funding from NHS North of Tyne, the UK National Institute of Health Research, and/or Newcastle University.
Hum Reprod. Published online April 5, 2011. Abstract
— Laurie Barclay, MD