1 TNO Prevention and Health, Leiden, PO Box 2215, 2301 CE, 2 Department of Obstetrics and Gynaecology, University Hospital St Radboud, Nijmegen, 3 Department of Obstetrics and Gynaecology, Leiden University Medical Center, Leiden, 4 Department of Obstetrics and Gynaecology, Diaconessen Hospital, Voorburg, 5 Department of Obstetrics and Gynaecology, University Medical Center, Utrecht, 6 Department of Obstetrics and Gynaecology, Isala Clinics, Location Sophia, Zwolle and 7 Department of Obstetrics and Gynaecology, Erasmus Medical Center, Rotterdam, The Netherlands
8 To whom correspondence should be addressed. e-mail: m.fekkes{at}pg.tno.nl
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: emotional functioning/health-related quality of life/IVF/psychological functioning/social functioning
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Several studies suggest that the impact of infertility and its treatment is higher in women than in men (Freeman et al., 1985; Callan and Hennessey, 1988
; Newton et al., 1990
; 1999
; Collins et al., 1992
; Oddens et al., 1999
). It may therefore be important to study men and women separately. To our knowledge the psychological status of people planning to undergo IVF has to date not been studied in different age groups and in men and women separately. Counselling could be offered to those groups of patients with less optimal functioning in order to improve their well-being.
If IVF clinicians are aware at the start of the treatment which subgroups are most likely to suffer high levels of distress, they may be more able to gear their counselling efforts towards these groups. Couples usually undergo several cycles of IVF treatment. However, if the first IVF attempt fails, a high level of emotional strain appears to be the main reason for not continuing with a new IVF cycle (Mahlstedt et al., 1987; Goverde et al., 2000
).
The concept of health-related quality of life may be a useful tool for discovering in which domains people planning IVF may have more problems than reported in the general population. It might also be hypothesized that some areas of health-related quality of life are influenced by the treatment in a positive way, since the start of the treatment could create hope and optimism, resulting in a better quality of life. Health-related quality of life as perceived by the patients themselves is increasingly being used to measure the impact of disease and the effects of treatment. It is widely accepted that health-related quality of life includes patients own perception of their functioning in four domains: physical functioning, emotional functioning, social functioning and cognitive functioning (Aaronson, 1988; Verrips et al., 1999
).
In the present study we adopted this concept of measuring health-related quality of life. The subjective judgement on the patients health (versus more objective measures such as, for example, blood pressure) and the broad scope of domains make health-related quality of life a useful tool in investigating which domains of health are affected.
We included the four domains in which a difference may occur between the group planning to undergo an IVF treatment and the general population. To measure these domains we used validated, generic and normed instruments that were available in the Dutch language.
The main research question we aimed to answer is whether health-related quality of life in couples planning IVF treatment differs from that in the general population, comparing different age subgroups as well as separate subgroups of men and women.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Procedure
During their visit to the IVF clinic couples were informed by their IVF physician about the aims of the study and were invited to participate. Couples that agreed to participate filled out a written informed consent form. Participants were subsequently mailed a set of questionnaires to their home. Each partner received a separate set of questionnaires. Completion of the questionnaires took on average 45 min. Respondents could send the completed questionnaires back to the researchers free of charge. A reminder letter was mailed if a participant did not return the questionnaires within 4 weeks. Participants who did not respond within 8 weeks were approached by telephone and asked again if they were willing to complete the questionnaires. Only participants who filled out the questionnaires before the start of their first treatment were included in the study.
Measures
Four outcome measures as outlined below were used in the study. Normative data from the general population were available for all measures except for the Irrational Parenthood Cognitions scale, which was developed by the authors.
The Hopkins Symptom Checklist
The Hopkins Symptom Checklist (HSCL) (Derogatis et al., 1974) is a 57-item measure that provides an assessment of psychological and physical discomfort. Respondents can indicate for each psychological or somatic complaint to what extent this applies for them, and each item is scored as: not at all (0), a bit (1), quite a lot (2), very much (3). Items are totalled into scales. As well as an overall scale, two subscales can be derived from this measure, and these subscales were used in our study. The 17-item psychological complaints subscale aims to measure psychological and neurotic complaints such as unpleasant thoughts, outbursts of anger, worrying and despair. The reliability of this scale, measured by Cronbachs
, was 0.88. Scores range from 0 to 51, with higher scores indicating more psychological complaints. The eight-item somatic complaints subscale aims to measure physical complaints such as headaches, dizziness, palpitations and backache. Cronbachs
for this scale was 0.73. Scores range from 0 to 24, with higher scores indicating more somatic complaints. Normative data are derived from Luteijn and colleagues (Luteijn et al., 1984
; F.Luteijn, personal communication). The normative group consists of a sample of adults from Dutch households that were drawn randomly from the telephone book.
The Sickness Impact Profile
The Sickness Impact Profile (SIP) (Bergner et al., 1981; Jacobs et al., 1990
; 1992
) is a 136-item measure that determines the influence of illness and/or health complaints on daily functioning. Respondents have to indicate for each item if it applies to them. Scale scores are derived by adding up the number of tagged items. Higher scores indicate more impact of the current health situation on the specific domain. Twelve subscales can be derived from this measure, four of which were used in this study. These subscales are emotional behaviour, measuring the emotional impact of the current health situation with items such as I am nervous or restless (scale range 09; Cronbachs
= 0.70); social interactions, measuring the impact of the health situation on social interactions with items such as I visit friends less often (scale range 020; Cronbachs
= 0.79); alertness behaviour measuring the impact of the current health situation on the alertness functioning with items such as I cannot keep my attention focused (scale range 010; Cronbachs
= 0.74); and communication, measuring the impact of the health situation on communication skills with items like When I talk I lose control over my voice (scale range 09; Cronbachs
= 0.71). Normative data are derived from Jacobs et al. (1990)
. The normative group consists of a random sample of Dutch adults who are participating in the National Health care plan.
The Irrational Beliefs Inventory
The Irrational Beliefs Inventory (IBI) (Koopmans et al., 1994) is a 50-item measure assessing irrational cognitions and is based on the Irrational Beliefs Test (IBT) (Jones, 1968
) and the Rational Behavior Inventory (RBI) (Shorkey and Whiteman, 1977
). This measure can be of use in cognitive interventions. The IBI contains items such as There is only one right way to do things, I want everybody to like me and If a person wants to, he can be happy under almost any circumstance. Every item can be scored on a five-point dimension ranging from I strongly disagree to I strongly agree. Item scores range from 1 to 5 and are added up to the total scale ranging from 50 to 250, with higher scores indicating more irrational cognitions. Cronbachs
= 0.89. Normative data are derived from Timmerman et al. (1993)
. The normative group consists of a random sample of the registered Dutch residents from one region in The Netherlands.
The Irrational Parenthood Cognitions scale
The Irrational Parenthood Cognitions (IPC) scale was developed by the authors of this work to measure specific irrational cognitions concerning the need to have children in order to live a happy life. The term irrational refers to the ideas of Ellis (1962). Ellis states that people at a young age may learn norms and values that are not necessarily realistic or consistent. These irrational ideas can lead to the development of emotional and psychological complaints. This scale contains 14 items. Examples are: A life without children is useless and empty or You start hating your body when you cannot have children. Respondents were asked to score on a five-point scale to what extent they agreed with these statements. The items were subsequently totalled to a scale score of 056, with higher scores indicating a stronger need to have children in order to live a happy life.
The reliability of this scale, measured by Cronbachs , was 0.84 for male respondents and 0.87 for female respondents. An English version of the IPC scale is presented in Appendix I.
Background variables
With a separate questionnaire, several background variables were measured such as: infertility diagnosis, duration of infertility, history of infertility treatments, presence of children in the family at the start of the IVF treatment, age of both partners and education level.
The following (sub)scales were used to measure the different dimensions of the concept of health-related quality of life. Emotional functioning: the SIP subscale emotional behaviour and the HSCL subscale psychological complaints. Cognitive functioning: the IBI total scale. Social functioning: the SIP subscales social interactions, alertness behaviour and communication. Physical functioning: the HSCL subscale somatic complaints.
Analyses
2 and ANOVA analyses were used to calculate differences in background variables between different age groups of the IVF sample.
Normative data from the general population were only available to us in tables with means and SEM or SD. This limited the options for analysis.
Two-sided Students t-test analyses compared the mean scale scores on the outcome variables for the IVF sample with the scores for the general population. This analysis was carried out separately for men and women. The analyses were subsequently carried out for different age groups (2130, 3140 and 4150 years), whereby men or women planning IVF were compared with adults of the same age group from the general population. The group of men >50 years of age and the group of women >40 years of age were not included in the analysis, since they were too small to allow a meaningful analysis to be performed. Owing to missing data the number of respondents included in the analyses differed per outcome measure.
Standard multiple regression (method enter) analysis was used to calculate the individual contribution of the background variables (i.e. age, infertility diagnosis, duration of infertility, education level and children present in the family) and irrational parenthood cognitions on the outcome measures. All independent variables were included in the model to calculate the partial correlation for each variable.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Of those who filled out the consent form, 425 men and 447 women (420 couples plus 32 individual men and women) returned the questionnaire. This yields an 82% response rate (84% of the women and 80% of the men). The mean age for women was 32 years (range 2143) and for men 36 years (range 2259).
Non-response analysis
The non-responders did not differ from the responders with regards to age, duration of infertility or the presence of children in the family. A difference did exist between the two groups in the distribution of the infertility diagnosis. The non-response group included more women with tubal pathology (25 versus 14%) and fewer patients with idiopathic infertility (10 versus 21%).
Characteristics of the sample
The distribution of background variables is presented for different age groups of men and women separately in Table I.
|
Emotional functioning
Emotional functioning was assessed with the emotional behaviour scale of the SIP, and with the psychological complaints subscale from the HSCL.
The SIP scores for the subscale Emotional behaviour in Table II show that women planning IVF exhibited more emotional behaviour problems than women in the general population. Within the youngest age group this difference was the largest. For the men planning IVF, the youngest age group demonstrated significantly more emotional behaviour problems compared with the general population. However, the older age groups of men planning IVF did not differ significantly from the general population.
|
Social functioning
Social functioning was measured with three SIP subscales: social interaction, alertness behaviour and communication. The mean scores on these scales for both the IVF and the general population (Jacobs et al., 1990) are also presented in Table II.
The SIP scores in Table II show that women planning IVF had more problems in social functioning than women in the general population. For younger women in particular, large differences were shown on all the three subscales social interaction, alertness and communication. Older women planning IVF reported more problems for two of these subscales, namely alertness and communication.
The youngest group of men planning IVF differed from the general population in a similar way to the youngest group of women planning IVF. On all three social functioning subscales young men planning IVF indicated higher problem scores than the general population. The older men planning IVF (3140 and 4150 years) did not differ on most of the social functioning subscales. Only on the subscale communication did the oldest group of men planning IVF show more problems than the general population.
Physical functioning
Perceived physical functioning was assessed with the psychosomatic complaints scale from the HSCL. Women planning IVF did not differ from the general population with regards to the HSCL scores for this subscale. This was the case for both age groups (data not shown). In men planning IVF the age group 2130 years reported fewer psychosomatic complaints than the general population (1.4 versus 2.7, t = 2.09, P < 0.05). For the other two age groups no significant differences were found (data not shown).
Cognitive functioning
Cognitive functioning was measured with the IBI total scale. The IBI scores indicated no significant differences between the IVF group and the general population.
Irrational parenthood cognitions and quality of life
Younger women (2130 years) had higher levels of irrational parenthood cognitions than women in the older (3140 years) age group (34.1 versus 29.2; t = 4.032; df = 402; P < 0.001). Among men, the irrational parenthood cognitions were also higher among the youngest age group compared with the oldest (4150 years) age group (29.2 versus 24.3; t = 2.645; df = 131; P = 0.01). The younger men (2130 years) had also higher irrational parenthood cognitions than 3140-year-old men (29.2 versus 25.8; t = 2.303; df = 320; P = 0.02).
A standard multiple regression analysis (method enter) was performed to determine the individual contribution of background variables and irrational parenthood cognitions on the scores on the quality of life outcome measures. All background variables were included in the model. The partial correlations presented in Table III indicate that a substantial part of the variance in quality of life outcome measures could be accounted for by irrational parenthood cognitions, when controlling for the influence of other background variables. For both men and women and on all outcome measures, a higher level of irrational parenthood cognitions was related to a higher level of problematic functioning. Partial correlations were especially high for womens scores on the scales emotional and social behaviour and psychological complaints. Other variables presented in Table III such as already having a child in the family, age and level of education, had significant correlations on some of the outcome measures, but these correlations were substantially lower. The other variables that were included in the regression model, i.e. duration of infertility and infertility diagnosis, had no significant partial correlations with any of the outcome measures.
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We found that women planning IVF, in particular young women aged 2130 years, experienced more social and emotional problems than women of the same age group in the general population. The group of young men planning IVF (aged 2130 years) also reported more social and emotional problems than a similarly aged group of men in the general population. These differences were somewhat smaller for men than for women. We found no difference in social and emotional functioning between the groups of relatively older men planning IVF and the general population. No substantial differences were found in cognitive and physical functioning for all age groups of men or women planning IVF compared with the general population.
It was shown from our data that within the subgroup of younger couples planning IVF, particularly the women reported lower health-related quality of life. This finding has been confirmed by other studies, which indicate that for women, more often than for men, infertility is one of the most upsetting experiences of their lives (Freeman et al., 1985) and is related to higher levels of anxiety (Slade et al., 1997
). However, the results of our study also show that at a group level the IVF patientsboth men and womenhave neither higher levels of cognitive or (psycho)somatic problems, nor higher levels of psychological complaints on the HSCL scale. In addition, relatively older men planning IVF did not differ from the general population with regard to emotional and social functioning.
The higher levels of problematic functioning for women planning IVF when compared with the general population are found only on scales of the SIP. No differences were found on the scale psychological complaints of the HSCL, measuring more long-term emotional problems. The SIP questionnaire determines the influence of illness and/or health complaints on daily functioning, indicating that this problematic functioning may be a short-term effect of the treatment that these patients are anticipating. Even if this is the case these higher levels of problematic functioning should be taken seriously. IVF treatments during which people feel anxiety and depression may lead to avoidance coping. When a first IVF attempt fails, negative feelings and avoidance may lead to discontinuing the treatment (Cook et al., 1989). Mahlstedt et al. (1987)
found that the main reason for couples not continuing IVF treatment was the emotional strain of the previous treatment cycle. Goverde et al. (2000)
recently reported a randomized clinical trial comparing IVF with intra-uterine insemination (IUI). Couples in the IVF programme were less likely to achieve pregnancy although the success rate per cycle was higher for IVF than for IUI. The main reason for this difference was that IVF couples discontinued treatment before the maximum number of cycles had been completed far more often than did couples in the IUI treatment arm.
The conclusion that especially younger men and women planning IVF have more problems compared with the general population may at first sight appear somewhat surprising. At the onset of our study we expected that older couples may have more stress-related problems, since for most of these couples IVF offers their very last chance of having a baby. Younger couples, on the other hand, have more time and may still have the option to apply for adoption. However, our results show that younger couples in particular indicated more stress-related problems. One explanation may be that these couples respond differently to the process of infertility diagnostic tests and/or treatments that they went through before entering into the IVF programme. Older patients do have a longer history of infertility and might be more able to cope with their medical situation because they have had more infertility-related experiences. Boivin et al. (1995) found that women with high amounts of treatment failures indicated less stress than women with moderate amounts of treatment failures.
It is also possible that the infertility itself is more stressful to younger than to older couples. In order to be in an IVF programme before the age of 29 years a woman must have started trying to become pregnant relatively early in life, especially by Dutch standards. Dutch women have the highest age at the birth of their first child of all women in Western countries, with an average age of 29.0 years in 1997 when this study was performed (CBS, 1999). Most women had tried to become pregnant for several years before entering into an IVF programme. Therefore, the group of young women planning IVF had a first attempt at starting a family at an earlier age than most Dutch women. Perhaps their outlook on a life without children is fundamentally different from that in older IVF couples. If indeed for these young IVF women raising children is their single most important role in life, not being able to have children may be more stressful to them than to older women, who may have had other priorities in the period of their lives before trying to start a family. The results of our study indicate that the younger IVF patients are a different group when compared with the older patients. Less often they already had children present in their family. The women in this younger age group had a lower educational level than IVF women in the older age groups, and both men and women in this group showed more irrational parenthood cognitions than did older couples planning IVF. This last result indicates that these patients have a stronger notion than other couples planning IVF that they need to have children in order to live a happy life.
It is confirmed by results in our study that irrational parenthood cognitions accounted for a substantial part of the scores on all quality of life outcome measures, more so than did other background variables like age or infertility history. High levels of irrational parenthood cognitions were related to less optimal functioning, especially for emotional and psychological functioning. Therefore, higher levels of irrational parenthood cognitions among the group of younger men and women may indeed be the most plausible explanation for their more problematic psychosocial functioning.
This intense focus on having a child is also found in other studies to be the predominant factor in anticipated stress of IVF treatment for both males and females (Collins et al., 1992). Newton et al. (1999)
found that both men and women with fertility problems who have a high need for parenthood and a strong rejection of a childfree lifestyle, also have more symptoms of depression and anxiety.
Counselling directed towards lowering the emotional strain may be an important measure to prevent couples from raised levels of problematic functioning and discontinuing from their treatment after a failed attempt. It is advised that therapeutic counselling is initiated before infertility treatment in order to provide patients with opportunities to learn the skills to cope with the infertility and the associated medical procedures (Lukse and Vacc, 1999). Our study showed that counselling should especially be directed towards those patients with high levels of irrational parenthood cognitions, which more often concerns younger women. Counselling may be directed towards changing the cognitions of those patients who are focused on the idea that having a baby is necessary to live a happy life and have high scores on related notions on the IPC scale. Such counselling may follow the principles of Rational Emotive Therapy (Engels et al., 1993
; Ellis, 1997
), in which patients learn to change their cognitions in order to change the negative emotional impact of these cognitions. Irrational cognitions have in other areas shown to be highly amenable to cognitive therapy. Longitudinal research is needed in order to determine whether counselling interventions will indeed enhance IVF couples quality of life and will decrease the chance of discontinuing treatments.
|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Berg, B.J. and Wilson, J.F. (1991) Psychological functioning across stages of treatment for infertility. J. Behav. Med., 14, 1126.[ISI][Medline]
Bergner, M., Bobbitt, R.A., Carter, W.B. and Gilson, B.S. (1981) The Sickness Impact Profile: Development and final revision of a health status measure. Med. Care, 19, 787.[ISI][Medline]
Boivin, J., Takefman, J.E., Tulandi, T. and Brender, W. (1995) Reactions to infertility based on extent of treatment failure. Fertil. Steril., 63, 801807.[ISI][Medline]
Bremer, B.A. and McCauley, C.R. (1986) Quality-of-life measures: hospital interview versus home questionnaire. Health Psychol., 5, 171177.[CrossRef][ISI][Medline]
Callan, V.J. and Hennessey, J.F. (1988) Emotional aspects and support in in vitro fertilization and embryo transfer programs. J. In Vitro Fert. Embryo Transfer, 5, 290295.[ISI][Medline]
CBS (1999) Statistisch Jaarboek 1999. Centraal Bureau voor de Statistiek, Voorburg/Heerlen, The Netherlands.
Collins, A., Freeman, E.W., Boxer, A.S. and Tureck, A.R. (1992) Perceptions of infertility and treatment stress in females as compared with males entering in vitro fertilization treatment. Fertil. Steril., 57, 350356.[ISI][Medline]
Cook, R., Parsons, J., Mason, B. and Golombok, S. (1989) Emotional, marital and sexual functioning in patients embarking upon IVF and AID treatment for infertility. J. Reprod. Infant Psychol., 7, 8793.
Derogatis, L.R., Lipman, R.S., Rickels, K., Uhlenhuth, E.H. and Covi, L. (1974) The Hopkins Symptom Checklist, a self-report symptom inventory. Behav. Sci., 19, 115.[ISI][Medline]
Ellis, A. (1962) Reason and Emotion in Psychotherapy. Lyle-Stuart, New York, NY.
Ellis, A. (1997) Albert Ellis on rational emotive behavior therapy. Am. J. Psychother., 51, 309316.[ISI][Medline]
Engels, G.I., Garnefski, N. and Diekstra, R.F. (1993) Efficacy of rational-emotive therapy: a quantitative analysis. J. Consult. Clin. Psychol., 61, 10831090.[CrossRef][ISI][Medline]
Freeman, E.W., Boxer, A.S., Rickels, K., Tureck, R. and Mastroiani, L. (1985) Psychological evaluation and support in a program of in vitro fertilization and embryo transfer. Fertil. Steril., 43, 4853.[ISI][Medline]
Glaser, A.W., Davies, K., Walker, D. and Brazier, D. (1997) Influence of proxy respondents and mode of administration on health status assessment following central nervous system tumours in childhood. Qual. Life Res., 6, 4353.[Medline]
Goverde, A.J., McDonnell, J., Vermeiden, J.P., Schats, R., Rutten, F.F. and Schoemaker, J. (2000) Intra-uterine insemination or in-vitro fertilisation in idiopathic subfertility and male subfertility: a randomised trial and cost-effectiveness analysis. Lancet, 355, 1318.[CrossRef][ISI][Medline]
Grootendorst, P.V., Feeney, D.H. and Furling, W. (1997) Does it matter whom and how you ask? Inter- and intra-rater agreement in the Ontario Health Survey. J. Clin. Epidemiol., 50, 127135.[CrossRef][ISI][Medline]
Jacobs, H.M., Luttik, A. and Touw-Otten, F.W.M.M. (1990) Overzichtstabellen Functionale Status Gegevens van een Open Populatie. Rijksuniversiteit Utrecht, Utrecht.
Jacobs, H.M., Luttik, A., Touw-Otten, F.W.M.M., Kastein, M. and de Melker, R.A. (1992) Measuring impact of sickness in patients with nonspecific abdominal complaints in a Dutch family practice setting. Med. Care, 30, 244251.[ISI][Medline]
Jones, R. (1968) A factored measure of Ellis irrational beliefs system with personality maladjustment correlates (doctoral dissertation, Texas Technical College). Diss. Abstr. Int., 29, 43794380.
Koopmans, P.C., Sanderman, R., Timmerman,I. and Emmelkamp, P.M.G. (1994) The Irrational Beliefs Inventory: development and psychometric evaluation. Eur. J. Psychol. Assess., 10, 1527.
Lukse, M.P. and Vacc, N.C. (1999) Grief, depression, and coping in women undergoing infertility treatment. Obstet. Gynecol., 93, 245251.
Luteijn, F., Hamel, L.F., Bouwman, T.K. and Kok, A.R. (1984) HSCL Hopkins Symptom Checklist. Handleiding. Swets & Zeitlinger, Lisse.
Mahlstedt, P.P., Macduff, S. and Bernstein, J. (1987) Emotional factors and the in vitro fertilization and embryo transfer process. J. In Vitro Fert. Embryo Transfer, 4, 232236.[ISI][Medline]
Newman, N.E. and Zopuves, C.G. (1991) Emotional experiences of in vitro fertilization participants. J. In Vitro Fert. Embryo Transfer, 8, 322328.[ISI][Medline]
Newton, C.R., Hearn, M.T. and Yuzpe, A.A. (1990) Psychological assessment and follow-up after in vitro fertilization: assessing the impact of failure. Fertil. Steril., 54, 879886.[ISI][Medline]
Newton, C.R., Sherrard, W. and Glavac, I. (1999) The fertility problem inventory: measuring perceived infertility-related stress. Fertil. Steril., 72, 5462.[CrossRef][ISI][Medline]
Oddens, B.J., den Tonkelaar, I. and Nieuwenhuyse H. (1999) Psychosocial experiences in women facing fertility problems a comparative survey. Hum. Reprod., 14, 255261.
Shaw, P., Johnston, M. and Shaw, R. (1988) Counseling needs, emotional and relationship problems in couples awaiting IVF. J. Psychosom. Obstet. Gynecol., 9, 171180.[ISI]
Shorkey, C.T. and Whiteman, V.L. (1977) Development of the Rational Behavior Inventory: initial validity and reliability. Educ. Psychol. Meas., 37, 527534.[ISI]
Slade, P., Emery, J. and Lieberman, B.A. (1997) A prospective, longitudinal study of emotions and relationships in in vitro fertilization treatment. Hum. Reprod., 12, 183190.[Abstract]
Timmerman, I., Sanderman, R., Koopmans, P.C. and Emmelkamp, P.M.G. (1993) Het Meten van Irrationele Cognities met de Irrational Beliefs Inventory: Een Handleiding. Noordelijk Centrum voor Gezondheidsvraagstukken, Groningen.
Verrips, E.G.H., Vogels, T.G.C., Koopman, H.M., Theunissen, N.C.M., Kamphuis, R., Fekkes, M., Wit, J.M. and Verloove-Vanhorick, S.P. (1999) Measuring health-related quality of life in a child population. Eur. J. Public Health, 9, 188193.[Abstract]
Submitted on March 8, 2002; resubmitted on December 20, 2002; accepted on March 17, 2003.