“Fathers of test tube babies may be passing on their infertility to their sons,” according to The Times.
This news story is based on research that looked at the finger lengths of children conceived with a form of IVF called intracytoplasmic sperm injection (ICSI) that can be used to overcome male fertility problems. Finger length is thought by some scientists to indicate the response to testosterone exposure in the womb. This research compared the finger lengths of ICSI children to those conceived naturally to try to predict future fertility.
This study was very small and measured finger lengths by looking at photocopies of prepubescent children’s hands. It was preliminary research and did not convincingly demonstrate that children of either sex conceived in this way would have fertility problems when they were older.
The speculative nature of this research means it should not be of concern to parents who have used ICSI or those hoping to use IVF. The researchers themselves say that there is a need fully assess the children once they are older.
Where did the story come from?
This study was carried out by Dr Alastair Sutcliffe and colleagues at University College London, and the University of Southampton in the UK and researchers in Germany. No external funding is reported. The study was published in the peer-reviewed medical journal Reproductive Biomedicine.
This was preliminary research but the press tended to overemphasise the conclusions that can be drawn from this study. As it stands, it is not possible to say that children conceived through ICSI will have fertility problems and further research is required.
The Daily Mail’s coverage has included a quote from Josephine Quintaville of the Comment on Reproductive Ethics focus group: “Using ICSI is obviously counterintuitive to good health and this research would demonstrate that may be true”. Contrary to what this comment might suggest, this study did not look at health risks related to IVF or report any adverse effects on health.
What kind of research was this?
This was a controlled study that compared finger lengths of children conceived naturally to those of children conceived using ICSI, a form of in-vitro fertilisation (IVF). In ISCI a technician will fertilise an egg cell by injecting it with a single sperm cell under a microscope. The technique is used in cases where the male has sperm problems such as ‘lazy sperm’ (immotile sperm) or a low sperm count.
Finger length is thought to be partially determined by testosterone exposure within the first 14 weeks of pregnancy, which is, in turn, governed by genes. The researchers explain that having disproportionately short fingers or a long index finger in relation to ring finger length has previously been observed in men who produce no sperm and men who are rated as having low sexual attractiveness.
The researchers in this study predicted that babies conceived using ICSI would be likely to carry the same fertility traits as their fathers and suggested that finger length in infants could be used to assess children’s future fertility. This research did not measure the finger lengths of the fathers.
This was a relatively small study. A larger study would be necessary to demonstrate that the differences observed were not just down to chance. The study did not follow-up the children to adulthood, which would have been a better approach to determine whether poor sperm quality is a genetic trait that is passed from father to son.
What did the research involve?
The study recruited German and British children aged four to nine years who had been conceived either naturally or through ICSI. In total there were 201 boys and 205 girls included in the study, of which 211 were conceived by ICSI and 195 naturally. The families were asked to send a photocopy of their child’s hand to the researchers, from which the researchers measured the length of the fingers. From these measurements they calculated the ratio of each child’s index finger length to their ring finger length.
What were the basic results?
The researchers measured the lengths of the children’s fingers in relation their height. After using statistical methods to adjust for the influence of height, they found that for their size all ICSI children had shorter ring and index fingers than the naturally conceived children.
There was overall no difference in the ratio of ring finger to index finger between the ISCI and naturally conceived groups. There was no difference in finger length ratio between the ICSI conceived males and the naturally conceived children, but females in the ICSI group had a greater ratio than the naturally conceived children.
How did the researchers interpret the results?
The researchers concluded that children born following ICSI had shorter fingers than the naturally conceived children and suggested that fathers with low sperm counts and low quality sperm tend to have shorter fingers for their height. They extrapolated this to suggest that boys could have a higher chance of having poorer quality sperm but highlight that it is not possible to draw any firm conclusions regarding future fertility in ICSI children.
This was a small study that tests the theory that finger length can predict male fertility. However, the study is very limited in addressing this question for a number of reasons:
- the age of the children means they could only have their fertility estimated and not tested directly,
- finger ratio is not universally accepted as an indicator of prenatal hormone exposure or adult fertility,
- the children’s fathers did not have their finger length measured to look for any associations with confirmed infertility,
- the study contained no information on the background of the children’s parents that may affect finger length, for example maternal smoking,
- the study was small in size and the associations seen may have occurred by chance.
The researchers do highlight that it is not possible to draw any firm conclusions regarding the fertility of ICSI children based on finger length alone, and that studies on post-pubertal boys are necessary to assess their fertility potential.
Since the advent of IVF, researchers have monitored the safety and long-term outcomes for children. This news should not concern parents who have used IVF to conceive or those with fertility problems, as this study has not indicated any health risks for children conceived using ISCI and does not warrant any changes in the provision of this treatment.
Links to the headlines
Infertile men are begetting infertile sons. The Daily Telegraph, February 9 2010
Test-tube boys may inherit fertility problems. The Times, February 9 2010
IVF fathers could pass infertility on to sons. Daily Mail, February 9 2010
Links to the science
Sutcliffe AG, Manningb JT, Katalanic A et al.Perturbations in finger length and digit ratio (2D:4D) in ICSI children. Reproductive BioMedicine Online Volume 20, Issue 1, January 2010, Pages 138-143