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  • Assisted reproduction affects children’s growth, but only in the first years

Research findings

Assisted reproduction affects children’s growth, but only in the first years

Published

Children born after assisted reproduction are smaller at birth, but grow faster during the first years of life, compared to naturally conceived children. At the age of 17, the differences are evened out, shows a new study from the Centre for Fertility and Health.

Two children holding each other
Children born after assisted reproduction are smaller at birth, but at the age of 17, the differences are evened out. Photo: Colourbox.com

Children born after assisted reproduction are smaller at birth, but grow faster during the first years of life, compared to naturally conceived children. At the age of 17, the differences are evened out, shows a new study from the Centre for Fertility and Health.


– The results are reassuring for parents who have had children after using assisted reproduction, says researcher Maria C. Magnus.

Together with colleagues, she has compared height, weight and body mass index (BMI) among children who have been conceived using assisted reproduction technologies with children who have been conceived naturally.

– We have known for a long time that babies born after assisted reproduction have a lower birth weight compared to naturally conceived children, but how long this difference in size persists has been unclear. It has also been unclear what role the underlying fertility problems in the parents may play in the difference in growth between children born after assisted reproduction and naturally conceived children.

Children born after assisted reproduction grow faster during the first years of life

The study included 81,461 children participating in the Norwegian Mother, Father and Child Cohort Study (MoBa), and 544,113 teenagers screened for military services and registered in the Armed Forces Health Register at the age of 17.

The researchers began by studying the growth of MoBa children up to 7 years of age. 79,740 of the MoBa children were naturally conceived, while 1,721 were born after assisted reproduction. Among the naturally conceived children, 5,279 were children of parents who had tried for more than 1 year to conceive.

Children born after assisted reproduction weighed an average of 3.495 grams and were 50.2 cm long at birth, while naturally conceived children weighed an average of 3,608 grams and were 50.5 cm long. Babies resulting from assisted reproduction grew faster than naturally conceived children in the first 18 months, and were slightly longer and heavier around 2 years of age, which persisted until 7 years of age.

Naturally conceived children of parents who had tried for more than 1 year to conceive were also smaller at birth than children of fertile parents, but not as small as the children born after assisted reproduction. They also had a growth pattern in the first years of life that resembled children born after assisted reproduction.

No difference at age 17

To study further development, the researchers used information from the Armed Forces' Health Register to compare height, weight and BMI at the age of 17 in all those screened for military service. They found no differences between those born after assisted reproduction and those who were naturally conceived.

– This suggests that children born using assisted reproduction regain some of their lost growth in the first years of life. More studies with longer follow-ups are needed to see if young adults born after assisted reproduction continue to develop similarly to naturally conceived children, says Magnus.

One explanation for the lower birth weight in babies born after assisted reproduction may be the hormones that the woman takes to stimulate ovulation or the growth medium in which the embryo develops. The study shows that characteristics related to the underlying fertility problems in parents likely also plays an important role.