18 November, 2008

Is there a cognitive cost of being a twin?

Multiple pregnancies have come under intense scrutiny because they are associated with prematurity and growth restriction. In developed countries, high rates of multiple pregnancies following assisted reproductive technology have been cited as a reason why preterm delivery rates remain stubbornly high and perinatal statistics have plateaued.

Long-term outcomes of twins take decades to be determined and it is described that twins born in developed countries half a century ago had lower IQs and academic performances than singletons. However, recent figures from Scandinavian studies show no differences between singletons and twins as measured by all cause mortality and academic achievement (Christensen & McGue BMJ 2008;337:a651:245-6). Perhaps modern antenatal care and catch-up interventions have nullified the discrepancies, but there is strong evidence that disadvantage no longer applies in these sophisticated environments.

It is of interest that a Taiwanese study of twins born in the mid-1980s shows that the subjects had lower academic achievements than singletons and had a lesser probability of attending college (Tsou et al pp 277-80). Is it possible that developing socio-economic factors play a role still, while these factors have been eradicated in developed countries?

HRT and quality of life

Women take hormone replacement therapy (HRT) to improve their quality of life. Symptoms such as hot flushes, sleep difficulties, vaginal dryness, unsatisfactory sexual function and emotional disturbances are the main indications for commencing HRT. These will remain the reasons for prescribing HRT despite the Women's Health Initiative trial casting doubt on the balance of benefits for women starting treatment 10 to 15 years after the menopause.


Another study running in parallel to the WHI trial was the women's international study of long duration oestrogen after the menopause (WISDOM) investigation (Welton et al BMJ 2008;337:a1190 (550-3). It was scuppered by the WHI results but there were sufficient data to look at quality of life outcomes over one year in women taking combined HRT or placebo. The domains in which the replacement therapy proved significantly better were vasomotor symptoms, sexual functioning, sleep problems, night sweats, vaginal dryness and aching joints or muscles. On the downside, more women complained of breast tenderness and vaginal discharge.


These women were also initiating treatment a considerable time after their menopause which is not ideal but the fact that they derived benefits restores some faith in the role of HRT in its primary function - symptomatic relief of hypo-estrogenic effects. There was no discernable influence on depression or other climacteric symptoms over the short-term. The jury is still out on the possible protective effects on cognitive function, protection from Alzheimer disease and cardio-vascular effects when HRT is started soon after menopause and continued for many years.


Another feature of HRT may be its effect on gastro-esophageal reflux. Jacobson et al (Arch Int Med 2008;168:1798-804) report on a large observational study in which women using estrogens were more at risk of experiencing heartburn than non-users. Their odds ratio was 1.66 and those taking combined HRT had only slightly less risk. The larger the dose and the longer the duration of use, the greater the likelihood of symptoms. The absolute risk is approximately 1 in 4 women will report such effects, and taking estrogens increases a woman's chances of being in the symptomatic category.