Risks for Stillbirth Relate to Baby Size

Stillbirths most common among very large and very small developing babies

(RxWiki News) Having a stillbirth can be one of the most devastating experiences that expectant parents could face. Sometimes it helps to understand the risk factors.

A recent study has found that babies at the greatest risk of being stillborn are those in the heaviest or lightest weight percentiles.

"Attend all prenatal visits with your OB/GYN or midwife."

The study was conducted by Joel Ray, MD, from the Departments of Medicine, Health Policy Management and Evaluation and Obstetrics and Gynecology at the University of Toronto's St. Michael's Hospital, and Marcelo Urquia, PhD, MSc, from the Center for Research on Inner City Health at St. Michael's Hospital.

Dr. Ray and Dr. Urquia looked at the birth records of all live-born babies and stillbirths in Ontario, Canada between 2002 and 2007.

A total of 767,016 babies were successfully born, and there were 4,697 stillborn infants, all delivered between the 20th and 41st week of pregnancy.

"Stillbirth" is usually defined as a baby who dies at the 23rd week of pregnancy or later and weighs at least 500 grams (1.1 pounds). The rate in most developed countries is about 6 stillbirths per 1,000 births, and more than half occur after the 27th week of pregnancy.

However, for this study, the researchers actually counted from the 20th week of pregnancy since this is when most pregnant women have had an ultrasound to look at the baby's developing bones and organs.

The researchers took into account the mother's age and how many children she had already had.

They found that the largest and especially the tiniest babies represented the largest percentage of babies who were stillborn.

For example, at 32 weeks of pregnancy, a baby who ended up being stillborn weighed an average 590 grams (1.3 ponds) for boys or 551 grams (1.2 pounds) for girls less than a baby who lived.

Further, 19 percent of stillbirths occur among babies in the lowest tenth percentile for weight.

At all number of pregnancy weeks studied, being at the extreme end of weight — whether weighing a lot or very little compared to other babies at that week — was a risk factor for stillbirth.

The researchers found that babies that are extremely tiny for their age in pregnancy weeks or who weigh less than 99 percent of other babies' average weight were 9.6 times more likely to be stillborn. They represented 6 percent of all stillbirths.

Similarly, babies in the top 1 percent for weight, who are exceptionally large for their age in pregnancy weeks, were about twice as likely to be stillborn and represented 1 percent of all stillbirths.

"As a possible hallmark of impending intrauterine death, severe small-for-gestational-age and large-for-gestational-age may each be potential targets for future stillbirth prevention initiatives," the authors wrote.

Dr. Ray said that an extremely small baby in the uterus can indicate a problem related to the woman's placenta, and an extremely large baby is often related to obesity or diabetes in the mother.

Dr. Ray noted that the existence of stillbirths – and their emotional impact on parents — tend to be largely overlooked by society despite the fact that they are more common than newborns' deaths from prematurity or conditions such as Sudden Infant Death Syndrome.

The study was published May 17 in the Journal of Perinatology. The research was funded by the Canadian Foundation for the Study of Infant Deaths. The authors declared no conflicts of interest.

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Review Date: 
August 17, 2012