Ultrasound Could Help Determine Fetuses at Increased Risk for Stillbirth

The smallest and the heaviest fetuses are at much higher risk of being stillborn than those of average weight, new ultrasound-imaging research has found.

Fetuses who are “severely small for gestational age,” or weigh below the bottom one percentile of all fetuses, disproportionately account for about 6% of all stillbirths, according to Canadian researchers. Fetuses that are “severely large for gestational age,” or weigh above the 99th percentile, account for nearly 1% of stillbirths.

“In this study of all registered live-born and stillborn infants in Ontario, extreme underweight and overweight states confer the highest risk of stillbirth,” said Drs. Joel Ray and Marcelo Urquia, from St. Michael’s Hospital (Toronto, Ontario, Canada), and authors of the article that was published in the July 2012 issue of the Journal of Perinatology.

Stillbirth is conventionally defined as the death of a fetus at more than 23 weeks of gestation weighing 500 g or more. However, Drs. Ray and Urquia included infants born beginning as early as 20 weeks of gestation on the grounds that maternal-fetal bonding is well established at that point, since most mothers-to-be have undergone a level 2 ultrasound detailing the unborn infant’s developing bones and organs.

Including those infants provides new data about the level to which low and high weights are linked with stillbirths, including those before the point of viability, according to Dr. Ray. That, then, may help clinicians better decide at which time it is better to allow a pregnancy to continue so the fetus can grow, or to deliver a premature baby who might otherwise die in the womb.

The rate of stillbirths in industrialized countries is approximately six per 1,000, of which half occur after 27 weeks of gestation. In poorer countries, the rate is up to five times higher. Stillbirths are more common than the death of a baby after birth, such as from prematurity or because of sudden infant death syndrome (SIDS). However, stillbirths have mostly been overlooked by medical professionals, especially in terms of their emotional effect on the mother, her partner, and extended family, according to Dr. Ray.

The researchers examined records of all 767,016 live births and all 4,697 stillbirths in Ontario between 2002 and 2007. They noted that because they looked at so many births, they could also make statistically precise estimations of the impact of extremely low birth weight on the risk of stillbirth.

The investigators discovered that 19% of stillbirths occur in fetuses under the tenth percentile of weight. But being below the first percentile of weight meant the fetus faced a 9.5 times higher risk of being stillborn than infants who are within the average weight range, between the 40th to 60th weight percentiles. Dr. Ray reported that when fetuses are severely small for gestational age, it typically means there is a problem with the placenta. Fetuses who are acutely large for gestational age are usually so because of the mom having diabetes or obesity.

The authors concluded that since more than 95% of women in the industrialized world receive a level 2 anatomic ultrasound scan before 22 weeks gestation, fetal weight should be estimated and reported at this time of the ultrasound, as a standard practice. In doing so, the early presence of a small or large fetus may help guide ongoing ultrasound monitoring for growth and well-being.

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