Growth patterns in ART children found different from those in naturally conceived

Published 24 February 2021

A large cohort study has shown that children conceived by ART are smaller at the time of delivery, experience a rapid catch-up growth, but are largely similar in height and weight to naturally conceived children at school age.

The influence of ART on healthy child development – physical, intellectual and mental – has been an ongoing concern which goes back to before the first IVF birth. Since then, an association between fertility treatment and adverse pregnancy outcomes has been well documented. A meta-analysis by researchers in China found a significantly increased risk of pre-term birth, low birth weight and small for gestational age; and a multicentre cohort study concluded that ICSI and IVF children need health care resources more than those naturally conceived.(1,2)

Less is known about how ART children continue to progress in terms of height, weight and body mass index when compared with those born without the help of fertility treatment. Now, a large ongoing long-term prospective cohort study has offered some clues by suggesting that fertility treatment may contribute to differences in growth patterns – at least in infancy – and that underlying parental subfertility may have an impact too.
However, the authors report that the ‘reassuring’ message for parents and clinics is that this effect does not persist beyond adolescence. Indeed, the growth patterns shown by ART children at the age of 17 are similar to those of their naturally conceived counterparts.

The findings are based on data from the Norwegian Mother, Father and Child Cohort Study (MoBa) on 81,461 singleton children (n = 79,740 naturally conceived; n = 1721 ART), and 544,113 teenagers screened for military service and entered in the Armed Forces Health Registry (which includes information on mode of conception).

For the MoBa children, researchers at the Norwegian Institute of Public Health in Oslo compared medical birth registry data according to mode of conception with maternally reported information from 18 weeks gestation to age seven. The ART children included those from fresh and frozen embryo transfer, while a small proportion (n = 5279) of the naturally conceived children were born to subfertile parents (<12 months to conception).(3)

The results showed that ART babies weighed less on average at delivery than those who were naturally conceived (3.495 kg vs 3.608 kg), and were shorter in length (50.2cm vs 50.5cm). However, those in all ART groups (ICSI, FET, etc) then experienced ‘rapid catch-up growth’, achieving greater height/weight by age three and a greater height by age seven. These growth patterns were similar among naturally conceived children born to the subfertile parents, although they were not as small as ART children at birth.

The study is also described as the first to show a difference in growth pattern in ART children up to school age. Compared with those naturally conceived, FET children were similar whereas those from fresh transfer ART were smaller; and FET children were longer/heavier for the first two years of life, and remained heavier up to age six. However, results for reported height, weight and BMI at age 17 from the Armed Forces Health Registry data were similar to those of all ART children.

So why do ART children grow differently in early life? While one likely explanation may lie in the ART procedures themselves (hormone treatments, culture media), the authors suggest the answer may also lie in ‘underlying factors influencing parental fertility problems’ given that the offspring from subfertile parents were also shown to have different growth patterns.

While the findings appear to allay concerns around growth rates overall, the need for follow-up research is clear according to the authors. Indeed, the authors in summarising their results report that ‘children conceived by ART are smaller at the time of delivery, experience a rapid catch-up growth, but are largely similar in length/height and weight to naturally conceived children at school age’, but go on to describe the term ‘catch-up growth’ as possibly misleading. They note that rapid weight gain in IVF children has been associated with raised blood pressure in teenage years and a greater risk of type 1 diabetes.(4,5) Thus, the potential cardiometabolic implications of accelerated growth rates among ART children in their first years of life should be investigated.

1. Qin J, Liu X, Sheng X, et al. Assisted reproductive technology and the risk of pregnancy-related complications and adverse pregnancy outcomes in singleton pregnancies: a meta-analysis of cohort studies. Fert Steril 2016; 105; 73-85.
2. Bonduelle M, Wennerholm U-B, Loft A, et al. A multi-centre cohort study of the physical health of 5-year-old children conceived after intracytoplasmic sperm injection, in vitro fertilization and natural conception. Human Reprod 2005; 20; 413–419;
3. Magnus MC, Wilcox AJ, Elin FA, et al. Human Reprod 2021; 36; deab007.
4. Ceelen M, van Weissenbruch MM, Vermeiden JP, et al. Pubertal development in children and adolescents born after IVF and spontaneous conception. Hum Reprod 2008; 23: 2791-2798. doi: 10.1093/humrep/den309
5. Norman E, Petzold M, Clausen TD, et al. Type 1 diabetes in children born after assisted reproductive technology: a register-based national cohort study. Human Reprod 2020; 35; 221-231.

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