Perturbations in finger length and digit ratio (2D:4D) in ICSI children

Effects of hand preference on digit lengths and digit ratios among children and adults

BACKGROUND

Prenatal sex hormones may not exclusively determine effects of hand preference on digit ratios. Genetic determination is an alternative possibility.

AIM

To study the likelihood of similar effects of hand preference on digit lengths and digit ratios.

METHODS

We selected similar numbers of left-handers and right-handers in samples of kindergarten children (N = 101, age range: 3.5-7 years) and adults (N = 189, age range: 17-28 years) and measured digit lengths (excluding the thumb) directly on the palmar hand.

RESULTS

Compared to right-handers, left-handers had longer digits and lower third-to-fourth (3D:4D) digit ratios among children, whereas an opposite pattern of handedness differences occurred among adults.

CONCLUSIONS

Effects of hand preference on digit lengths and ratios might be genetically/ontogenetically determined. Also discussed are implications of this set of findings for digit ratio research.

Normalized second and fourth finger lengths in male and female partners and IVF cycle outcomes

RESEARCH QUESTION

Hox genes are involved in limb formation during normal embryological development. Their modulation by circulating maternal oestrogens and androgens determines the length of the second and fourth fingers of the adult hand. Do these same intrauterine hormone levels also determine fertility outcomes in the adult?

DESIGN

To study the association between the length of the second and fourth fingers of both partners undergoing IVF (as a surrogate of their previous intrauterine exposure to oestrogens and androgens) with treatment outcome after IVF, data corresponding to 256 IVF cycles were analysed. Finger length was normalized to the individual height.

RESULTS

In the female partner, a longer normalized second finger length of the left (2DLN) hand, reflecting a high intrauterine exposure to oestrogens, was independently and significantly (P = 0.011) associated with obtaining at least one top-quality embryo in a multivariate model. Conversely, in the male partner a longer normalized fourth finger length of the left hand (4DLN), reflecting a high intrauterine exposure to androgens, was independently and significantly (P = 0.032) associated with obtaining at least one top-quality embryo in the same multivariate model. In the female partner, 2DLN was inversely and significantly (P = 0.01) associated with achievement of pregnancy.

CONCLUSIONS

Intrauterine exposure to high levels of oestrogens and androgens in females and males, respectively, predisposes to the production of higher-quality embryos under in-vitro conditions during adulthood. Paradoxically, this also seems to result in a lower pregnancy rate.

Time-to-pregnancy and offspring finger-length ratio (2D:4D)

OBJECTIVES

Time-to-Pregnancy (TTP) is an epidemiological tool to assess couple fecundity. The finger digit ratio (2D:4D) has been suggested as a marker of androgen exposure in utero. Maternal, paternal, or couple-mediated factors related to fecundity may also have an effect on androgen exposure during pregnancy. We aimed to investigate the association between TTP, infertility, or use of Assisted Reproductive Technologies (ART) and offspring 2D:4D.

METHODS

Data from 673 mother-child pairs were collected from questionnaires in the Maternal-Infant Research on Environmental Chemicals (MIREC) study across 10 cities in Canada. The mean maternal age was 33.4 years (SD 4.7), with a median gestational age of 12.1 weeks (SD 1.3), at the time of recruitment. Our study included 338 girls and 335 boys, and the mean age of the children at follow-up was 3.5 years (SD 1.0). TTP was assessed through questionnaires during the first trimester of pregnancy. Digital photographs of both hands were taken in a follow-up study to calculate the children's 2D:4D (2-5 years). anova, t tests, and multiple linear regression analyses were conducted.

RESULTS

Boys had significantly lower mean 2D:4Ds (0.936 ±0.041 in right hand, 0.936 ±0.040 in left hand) compared to girls (0.948 ±0.038 in right hand, 0.945 ±0.038 in left hand). The mean 2D:4D did not differ according to TTP, infertility, or use of ART. The only factors associated with the child's 2D:4D were the child's age and maternal 2D:4D.

CONCLUSIONS

Our study does not support an association between TTP, infertility, or use of ART and children's 2D:4D.

Female digit length ratio (2D:4D) and time-to-pregnancy

STUDY QUESTION

Is the female 2th- to 4th-finger ratio (2D:4D) associated with fecundity as measured by time-to-pregnancy (TTP)?

SUMMARY ANSWER

Our study does not support an association between female 2D:4D and TTP.

WHAT IS KNOWN ALREADY

The 2th- to 4th-finger ratio (2D:4D) has been proposed as a potential indicator of greater androgen exposure during fetal development. Women exposed in utero to unbalanced steroid hormones may have impaired fecundity in the adulthood. Fecundity is often measured by TTP, an epidemiological tool commonly used to assess the impact of environmental factors in human conception.

STUDY DESIGN, SIZE, DURATION

The Maternal-Infant Research on Environmental Chemicals (MIREC) Study is a pregnancy and birth cohort of 2001 women recruited before 14 weeks of gestation in 10 cities across Canada between 2008 and 2011. The present analysis is part of MIREC-CD Plus, a follow-up study in a subsample of some 800 MIREC mothers and their children from 2012 to 2015.

PARTICIPANTS/MATERIALS, SETTING, METHODS

TTP and maternal characteristics were collected from questionnaires administered during the first trimester of pregnancy as part of the MIREC study. Digital pictures of the ventral surface of both hands were obtained in the MIREC mothers at the MIREC-CD Plus follow-up study. The 2D:4D was calculated as the ratio of the second and fourth fingers of each hand. The exposure of interest was the 2D:4D of the women categorized by tertiles, or dichotomized as ≥1 (index finger longer than the ring finger) or <1 (ring finger longer than the index finger, implying greater androgen exposure during fetal development). The final sample included 696 mothers. Statistical analyses included discrete-time Cox proportional hazard models, allowing adjustment for potential confounding factors.

MAIN RESULTS AND THE ROLE OF CHANCE

There was no evidence of diminished/increased fecundability according to the 2D:4D, neither on the right nor on the left hand. In our analysis by tertiles, the smallest 2D:4D (i.e. higher androgen exposure during fetal life) resulted in FORs higher than 1 (i.e. shorter TTP) in both hands, although this was not statistically significant (FOR 1.19 [95% CI 0.93, 1.51] in the right hand and 1.16 [95% CI 0.91, 1.47] in the left hand). In the dichotomous analysis, 2D:4D <1 resulted in FORs higher than 1 (i.e. shorter TTP), but this was also not statistically significant (FOR 1.08 [95% CI 0.88, 1.33] in the right hand and 1.14 [95% CI 0.92, 1.42] in the left hand). Our large sample size resulted in a high statistical power to exclude an association between female 2D:4D and TTP.

LIMITATIONS, REASONS FOR CAUTION

The MIREC Study is a cohort of pregnant women, and therefore, women with infertility were excluded by design from our study.

WIDER IMPLICATIONS OF THE FINDINGS

Our data do not provide evidence for an association between female 2D:4D and fecundity as measured by TTP. Whether the female 2D:4D is a marker of in utero androgen exposure and whether it is associated with fecundity have yet to be determined.

STUDY FUNDING/COMPETING INTEREST

The MIREC Study was funded by Health Canada's Chemicals Management Plan, the Canadian Institute of Health Research (CIHR grant # MOP - 81285), and the Ontario Ministry of the Environment. MIREC-CD Plus was funded by Health Canada's Chemicals Management Plan Research Fund. The 2D:4D component was funded by a research grant from the CIHR-Quebec Training Network in Perinatal Research (QTNPR). M.P. Vélez was supported by a CIHR Fellowship Award, and a QTNPR scholarship. P. Monnier is supported by the Research Institute of the McGill University Health Centre. W.D Fraser is supported by a CIHR Canada Research Chair. There are no conflicts of interest to declare.

Outcomes for offspring of men having ICSI for male factor infertility

Since the introduction of intracytoplasmic sperm injection (ICSI) using single sperm isolated from testicular tissue in men with obstructive and non-obstructive azoospermia, or using ejaculated sperm in those with poor semen quality, there have been concerns that this might have adverse effects on the offspring compared to conventional in vitro fertilisation (IVF) and natural conceptions. ICSI is done for reasons other than male factor infertility, and on the whole has not been shown to have any more negative effects than those seen with IVF. There have however, been very few studies of ICSI with a focus on, or large enough numbers to examine, the specific outcomes associated with male factor infertility. From the limited information available in relation to the source of the sperm and aetiology of infertility in the presence of ICSI, there appears to be no increased risk of congenital malformations. There is, however, a small increase in both de novo and inherited chromosome abnormalities. In terms of growth and neurodevelopment, there are very few studies, and so far, no adverse outcomes have been found in young children whose fathers have a sperm defect. The origin of the sperm used in ICSI does not have a major influence on the early life outcomes for the offspring, but transgenerational and epigenetic effects remain unknown. When the male factor infertility is known or thought to be due to a Y-chromosome deletion, this information should be given to the young male offspring at a time that will ensure his own reproductive health and plans are optimized.

Second to fourth digit ratios, male genital development and reproductive health: a clinical study among fertile men and testis cancer patients

Second- to fourth-digit length ratio, 2D:4D, is a marker of testosterone level during foetal life that was found associated with sperm concentration or testosterone levels in some studies, but not in others, a difference possibly related to the way the ratio is assessed. In this study, 2D:4D was assessed in 122 men partners of pregnant women and in 71 testicular cancer patients using a new method based on direct measurements of finger lengths. In addition, we investigated the association between 2D:4D, birth weight, testicular volume, semen quality and time to pregnancy. A validation study of the method demonstrated high reliability and reproducibility. Neither digit lengths nor 2D:4D significantly differed in both groups of men. We found a significant negative association between 2D:4D and birth weight in testicular cancer patients. In fertile men, 2D:4D was associated with testicular volume (r=-0.36, p<0.001), total sperm number (r=-0.18, p=0.04) and time to pregnancy (r=0.24, p<0.02). In addition, participants with a history of epididymal cyst had a significantly higher 2D:4D than those without cysts. In conclusion, all significant findings indicate that the human male reproductive function is negatively related to 2D:4D. However, 2D:4D for testicular cancer patients does not point to a hormonal imbalance during foetal life as the common cause for developing germ-cell cancer. Such results obtained, thanks to an easy, direct and reliable method for measuring finger lengths, suggest the usefulness of this new tool in fertility studies as well as for studying men with developmental disorders of the reproductive tract.