It has been firmly established that stress during the early years of development can stunt a child’s physical and mental growth. Doctors have suspected that this vulnerability to stress begins in the womb, but conclusive evidence has remained elusive. A study by Dr. Ali Khashan, published in this month’s issue of Psychosomatic Medicine, helps strengthen the case.

Dr. Khashan utilized Denmark’s well-organized citizen records to examine 1.38 million births between 1979 and 2002. These births were correlated with records of deaths or serious illnesses in the family during pregnancy or in the period 6 months before conception, when the stress of the tragedy might linger to affect the fetus. A death in the family reduced the average birth-weight of the child by 27 grams. It also increased the risk of the child being severely underdeveloped (defined as a birth-weight below the 5th percentile) by 22%.

Children born significantly underweight face a much higher risk of sickness and impaired development, so this 22% elevation of likelihood is a cause for concern. This study suggests that mothers would be wise to take measures to reduce their stress, such as relaxation techniques or counseling. However, it cannot confirm that the elevated risk really is the direct result of stress because it is also possible that deaths or illnesses in the family interfered with logistical concerns like eating a healthy diet. Future studies may be able to settle this issue by controlling for lifestyle changes and actually testing mothers for stress hormones rather than using deaths in the family as a proxy for stress.