Female reproductive ageing is a complex trait mostly explained by a combination of genetic and non-genetic factors. It compromises the decline in the number of oocytes (quantity) and the decrease of oocyte quality. It has been postulated that BRCA1/2 gene mutation carriers have a lower quantitative ovarian reserve status. However, data from adequately powered clinical studies are lacking. The aim of the first part of this thesis is therefore to explore whether women with a BRCA gene mutation actually have a diminished quantitative ovarian reserve status. The putative role of BRCA genes on ovarian reserve decline was evaluated by the following outcomes: age at natural menopause, serum anti-Müllerian hormone (AMH) levels and number of mature oocytes in in vitro fertilisation (IVF) treatment. Based on this thesis and previous research, there is no sound evidence that BRCA mutation carriers have a reduced quantitative ovarian reserve status as compared to proven non-carriers or controls. However, various types of selection bias that go along with the study population complicate such comparison. At this moment, counselling of healthy mutation carriers should not be extended with information regarding fertility issues. The second part of this thesis focusses on the (cost)-effectiveness of individualised follicle stimulating hormone (FSH) dosing based on ovarian reserve testing (ORT) in IVF and intracystoplasmic sperm injection (ICSI) treatment. The ovarian response to controlled ovarian stimulation is an expression of the quantitative ovarian reserve. A large proportion of women show a poor or hyper response, which both have been shown to negatively affect live birth rates. As the antral follicle count (AFC) and AMH level are currently the best tests to predict such an inappropriate response, follicle stimulating hormone (FSH) dose individualisation based on one of these tests seems promising in order to improve the proportion of normal responses. It has been hypothesised that an increase in the proportion of normal responders may improve live birth rates. Nowadays, individualised FSH dosing is implemented in standard clinical care in many centres. However, it is still unclear whether such an approach indeed leads to better IVF/ICSI results and whether it is cost-effective. This thesis demonstrates that individualised FSH dosing based on AFC in women with a regular cycle does not increase live birth rates or improve treatment costs as compared to a standard FSH dose. This result was also found in predicted poor responders only. So, a standard dose of 150 IU/day is suitable for all women, with a regular menstrual cycle, starting their first IVF/ICSI treatment as it is less expensive and gives comparable live birth rates. In predicted hyper responders, individualised FSH dosing might have a positive effect on safety outcomes, but further adequately powered research is needed.