Ovulation Induction

Time to pregnancy and multiple births

BACKGROUND

Mothers of multiples are alleged to be more fecund than mothers of singletons. Some authors have suggested monitoring twinning rates for assessing temporal changes in a population's reproductive health.

METHODS

Using a nested case-control design, we estimated the odds of a multiple birth in relation to fecundity in the US Collaborative Perinatal Project inclusive of 8546 pregnant women who reported a known time-to-pregnancy (TTP) upon enrolment in the cohort, 1959-1966. Case mothers comprised 81 women giving birth to twins/triplets; control mothers comprised 243 women giving birth to singletons matched to case mothers on maternal age at a ratio of 3:1. The odds ratio (OR) for a multiple birth within 6 months of trying adjusting for maternal age and prior pregnancies was estimated using logistic regression. Discrete time Cox regression analysis was also utilized to estimate the fecundability OR.

RESULTS

Women with a TTP of <or=6 months were more likely to have a multiple birth than women reporting a TTP of >6 months [OR=1.95; 95% confidence interval (95% CI)=1.09-3.51]. Excluding pregnancies after 13+ months resulted in a loss of precision (OR=2.14; 95% CI=0.90-5.04).

CONCLUSIONS

These data support higher fecundity among mothers of multiples than mothers of singletons.

Anti-oestrogens: their clinical physiology and use in reproductive medicine

The anti-oestrogens are important both as therapeutic agents in reproductive medicine and as tools to investigate the physiology of the oestrogen receptor and hormonal control mechanisms. Clomiphene occupies the oestradiol receptor and, although initially stimulatory, has a net antagonistic effect as oestrogen receptors are not replenished. The major fertility-enhancing effect is to cause an increase in LH and FSH output by increasing the frequency of pulsatile output of these hormones. Many effects due to an anti-oestrogenic effect have been postulated; some, such as an adverse effect on cervical mucus, have been proven. The clinical use of the anti-oestrogens is outlined in Table 1. In well chosen patients a rewarding pregnancy rate is obtained with minimal intervention and few important side-effects. The challenge for the reproductive biologist is successfully to manage the patient who is clomiphene-resistant, either because of failure to ovulate or failure to conceive once ovulation is induced.