author={Judith G Hall},
  journal={The Lancet},
Twinning has fascinated human beings over the centuries. New technologies and large study groups have led to improved documentation of frequency and complications in twin pregnancies and long-term outcomes. Artificial reproductive technologies have led to a pronounced rise in numbers of dizygotic and monozygotic twins. Although spontaneous dizygotic twinning is clearly associated with increased concentration of follicle-stimulating hormone and ovulation of more than one egg, causes of… Expand
Monozygotic twinning associated with assisted reproductive technologies: a review.
An improved understanding of the factors that contribute to increased MZ twinning associated with ART will help to elucidate the poorly understood mechanisms involved in the process and will further aid in reducing the overall incidence of multiple pregnancies with their associated risks following ART procedures. Expand
Fecundity and twinning. A study within the Danish National Birth Cohort.
A long TTP is associated with a reduced risk of twinning, and women not planning a pregnancy had a lower rate of opposite sex twins than planners, but a comparable rate of same sex twins. Expand
How Does the Inclusion of Twins Conceived via Fertility Treatments Influence the Results of Twin Studies?
Estimates of genetic and environmental influences obtained from twin studies over the last 10–15 years are more or less unaffected by the inclusion of twins conceived via fertility treatments in their samples. Expand
On the origin of zygosity and chorionicity in twinning: evidence from human in vitro fertilization
The current knowledge is documented, the accepted dogma is criticized, and new insights are proposed into the origin of zygosity and chorionicity are proposed. Expand
The incidence of monozygotic twinning following PGD is not increased.
The incidence of MZ twinning was not increased in PGD compared with regular ICSI with blastocyst transfer, and this information is useful in counselling patients about potential risks of PGD. Expand
Risk of Monozygotic Twins After Assisted Reproduction: A Population-Based Approach
The present population based study suggests that the risk of monozygotic twin is about 60% higher among assisted than after natural conception. Expand
Twins born following fertility treatment: implications for quantitative genetic studies.
The differences found between ART and NC twins on group means and twin correlations suggest that researchers should be aware that including ART twins may influence results from twin studies. Expand
Twins Born Following Fertility Treatment: Implications for Quantitative Genetic Studies
Abstract The rate of multiple births is substantially elevated in women who have had assisted reproduction treatment (ART; ˜26%) compared to the general population (˜1%), and these offspring areExpand
An age-dependent ovulatory strategy explains the evolution of dizygotic twinning in humans
It is shown that the most successful ovulatory strategy would be to always double ovulate as an insurance against early fetal loss, but to never bear twins, which supports the hypothesis that twinning is a by-product of selection for double ovulation rather than selection for twinning. Expand
Major Discordant Structural Anomalies in Monochorionic Twins: Spectrum and Outcomes
It is shown that a wide spectrum of major discordant structural anomalies can be found in monochorionic pregnancies, and the outcome for the anomalous twin is poor, while the survival rate for the normal co-twin was 71%, with a favorable overall prognosis. Expand