By Margarita Nahapetyan
Women who are obese while being pregnant have significantly greater risk of delivering babies with certain birth defects, than women with normal weight, according to a new report.
Obese women are almost twice as likely to have a baby with neural tube defects, which are caused by the incomplete development of the brain or spinal cord, according to the study. For one such defect, spina bifida, a failure of the spine to close during early pregnancy, the risk more than doubled. The researchers also discovered the increased chances of developing other defects, such as heart problems, cleft lip and palate, fluid in the brain and problems in the growth of arms and legs.
Birth defects are a main reason of still birth and infant death, causing as many as 1 in 5 child mortality in the United States, according to background information in the study.
It has been a known fact for a long time that extreme weight during pregnancy can lead to gestational diabetes, hypertensive disorders, an increased risk of blood clots, a higher risk of infection, and an increased risk of C-section delivery. Children born to obese mothers are at high risk of being too large and also have an increased risk of perinatal death.
"It is important to note that birth defects are a rare event and occur in 2 to 4 per cent of pregnancies, so the risk remains very low," says Judith Rankin, PhD, a study co-author and a reader in material and perinatal epidemiology at the University of Newcastle in England. "The last thing we want to do is to scare women."
The new report, published in the latest issue of Journal of the American Medical Association, is a review of previously published study. Rankin and her team reviewed 18 studies that looked at the relationship between a woman's weight and her child's health, and compared them with the findings of 39 other studies to determine if there was still an association between obesity and birth defects.
The results showed that the risk of spina bifida was more than twice as high for obese mothers-to-be, and the overall risk of neural tube defects was 87 per cent higher for obese mothers compared with women with normal weight. The researchers also found that he risk of heart problems was 30 per cent higher, the risk of cleft lip and cleft palate, no matter together or separately, was about 20 per cent higher, the risk of hydrocephaly (buildup of water in the brain) was 68 per cent higher, and limb reduction abnormalities were 30 per cent higher for obese moms.
The definitions of overweight and obese that have been used in the study, were those set by the World Health Organization -- a body mass index, or BMI of 25 and more for overweight and 30 and more for obese. BMI is being calculated with a math formula that uses weight and height of a person.
Yet, it is not known for sure as to how exactly obesity increases the risk of birth defects, but Rankin and her colleagues came up with some possible explanations for the connection between obesity at conception and a higher risk of birth defects:
1. Obesity is a strong risk factor for type 2 diabetes, and maternal diabetes is known to increase the risk of birth defects, especially of the central nervous system and the heart.
2. Performing ultrasounds of heavy pregnant women is much more difficult, and birth defects may not be seen early in pregnancy. Therefore, obese women might not terminate pregnancies because of fetal defects as often as women with normal weight.
3. It was found that obese pregnant women have nutritional deficiencies, especially reduced levels of folate, which is very important in preventing neural tube defects. Mothers-to-be are advised to take 400 mcg of folic acid per day in order to get protection against spina bifida, and obese women may need more than the regular recommended dosage to prevent birth defects.
"This is the first time that so many studies have been combined to build a more accurate picture and it shows a link between a mother's weight and many of these serious conditions in the newborn baby. Given that we are seeing an increase in the number of people who are overweight or obese, then we may see an increase in the number of babies born with abnormalities", said Dr Rankin and added in the conclusion that more research is still needed to establish the link between extreme weight and birth defects for overweight women as there is not the same amount of research evidence for overweight as there is for obesity.