Women's knowledge of and attitudes to first and second trimester screening for Down's syndrome
Correspondence: Dr E. M. Wallace, Department of Obstetrics and Gynaecology, Monash University, Monash Medical Centre, 246 Clayton Road, Clayton, Victoria 3168, Australia.
One hundred women were interviewed at their first hospital antenatal visit to assess their knowledge of, and attitudes to, first versus second trimester screening for Down's syndrome. Overall, the women had limited knowledge of Down's syndrome, and the prenatal screening and diagnostic tests that are available. However, when informed, the majority of women expressed a clear preference for first trimester screening tests for Down's syndrome, regardless of the rate of miscarriage of Down's syndrome pregnancies between 10 and 15 weeks of gestation. These findings have implications for the planning of prenatal Down's syndrome screening programmes.
With a birth incidence of approximately 1.3 per 1000, Down's syndrome is the most common known cause of severe mental retardation in the developed world. Not surprisingly, prenatal screening for Down's syndrome in early pregnancy is now an established and valued component of modern antenatal care in most developed and many developing countries, representing a cost effective public health intervention. Currently, the most widely used screening strategy is second trimester maternal serum screening, which derives individual risks of fetal Down's syndrome from maternal age and maternal serum levels of various biochemical markers measured in the early second trimester of pregnancy. It has been calculated that by using the most effective second trimester marker combinations, this approach will detect 75% of Down's syndrome pregnancies for a 5% diagnostic rate1,2.
Over recent years, advances in both ultrasound3, biochemistry4 and the combination of both5 have afforded a progressive trend towards earlier screening for Down's syndrome, reflecting the anticipated benefits of earlier diagnosis and pregnancy termination, if indicated. However, two-thirds of Down's syndrome pregnancies will miscarry spontaneously and as many as 15–20% could miscarry between episodes of first and second trimester screening6,7. The continued development of first trimester screening may therefore expose many more women to choices regarding pregnancy termination than currently occurs with second trimester screening. While the opinions and attitudes of obstetricians towards prenatal screening and diagnosis and towards termination of pregnancy have been reported8, little has been published relating the attitudes and preferences of women regarding first versus second trimester Down's syndrome screening9. We undertook this study to explore women's preferences for first or second trimester screening, specifically with a hypothesis that most women, when informed of the miscarriage rates of Down's syndrome pregnancies, would prefer to delay screening until the second trimester.
One hundred English-speaking women who indicated an interest in having prenatal screening for Down's syndrome were interviewed at their first hospital antenatal visit by one of the investigators (S.M.) using a structured questionnaire. Each interview lasted approximately 15 minutes. The study had approval of the Human Research and Ethics Committee of the Monash Medical Centre.
There were two sections to the questionnaire. The first section, intended to assess existing knowledge, comprised 12 questions about Down's syndrome and the available screening and diagnostic tests. The second section comprised seven questions, exploring attitudes and preferences to first and second trimester screening. Specifically, attitudes to screening in light of the high miscarriage rates for Down's syndrome pregnancies were determined by assessing preferences for screening in a number of hypothetical scenarios where the risk of miscarriage of an affected pregnancy detected by nuchal translucency varied from 1 in 1 to 1 in 1000. Importantly, prior to administering this second section of the questionnaire, each woman was given structured information about Down's syndrome and the available tests (including detection and screen positive rates for the screening tests and excess miscarriage risks for the diagnostic tests). The interviewer also checked to ensure that each individual had understood the information prior to proceeding. The questionnaire also included general questions that provided background information on the ethnicity and level of education of the women. Simple descriptive statistics were used to describe the women's knowledge and to report their preferences for specific Down's syndrome screening tests.
The median age (range) of the women was 29 years (19–42). The median gestation (range) at interview was 10 weeks (6–14). Sixty-three women were white Australian, 17 white European, 14 Southeast Asian, three Middle-Eastern, two South American and one North African. Fifty-five women had completed tertiary education and the remainder secondary education. The women had very limited prior knowledge of Down's syndrome and of the potential screening and diagnostic tests that are available. Table 1 details some of the data relating to knowledge.
Table 1. Women's knowledge of Down's syndrome and prenatal testing at the first hospital antenatal appointment. Values are given as n.
|Were aware/ had heard of Down's syndrome||90|
|Knew that Down's syndrome was a chromosomal abnormality||34|
|Knew that Down's syndrome was associated with physical handicap||65|
|Knew that Down's syndrome was associated with intellectual handicap||44|
|Knew that the risk of miscarriage of a Down's syndrome pregnancy was higher than normal||1|
|Aware of any prenatal screening or diagnostic test||74|
|Aware of second trimester serum screening||38|
|Aware of nuchal translucency||37|
|Aware of amniocentesis||62|
|Aware of chorion villus sampling||15|
When given the choice of first or second trimester screening tests, assuming identical detection rates for both tests, the majority of women interviewed (n= 74) chose nuchal translucency in preference to second trimester serum screening. The reasons given for this preference included: it was an earlier test (n= 23); they were able to see their baby (n= 20); it provided an opportunity to detect other abnormalities (n= 10); they disliked blood tests (n= 15); and it was perceived to be an ‘easier’ test (n= 6). The reasons given by the 26 women who expressed a preference for second trimester serum screening over nuchal translucency included risks of ultrasound (n= 7); more accurate test (n= 9); and ‘easier’ test (n= 10). These preferences were then re-explored with the supplementary information that many Down's syndrome pregnancies miscarry between 10 and 15 weeks of pregnancy and that nuchal translucency may preferentially identify such pregnancies10. Identical detection rates of the two tests were still assumed. Sixty-nine women would still choose nuchal translucency, even if all of the Down's syndrome pregnancies detected by nuchal translucency miscarried before the second trimester. The reasons given included a desire to know the cause of the miscarriage and a desire to know if Down's syndrome was present, regardless of the outcome of the pregnancy. Some of these women also expressed value in a test that would predict miscarriage. A further 22 women would choose nuchal translucency, even if half of the affected pregnancies detected by this test miscarried before 15 weeks of gestation. The cut off miscarriage rate at which the remaining nine women would choose to have the later rather earlier screening test, was one each at 1 in 3, 1 in 4, 1 in 20, 1 in 50 and five at 1 in 1000.
When the possible implications of a chromosomal abnormality in one pregnancy on the management of subsequent pregnancies were outlined to the women, six women changed their stated preference for a screening test. In all cases the women indicated that they would be more likely to have the earlier screening test, stating that they would choose to have an early diagnostic test in a subsequent pregnancy.
To our knowledge this is the first study to explore women's preferences for first or second trimester Down's syndrome screening against the background knowledge of selective miscarriage of affected pregnancies. Contrary to our hypothesis, the majority of women stated a clear preference for the earliest possible screening test, even if this test only identified pregnancies destined for spontaneous loss before 15 weeks of pregnancy.
We were not surprised that most of the women interviewed (74%) would choose nuchal translucency over second trimester serum screening. Kornman et al.9 have previously shown that a similar proportion of Dutch women who chose to have second trimester serum screening would prefer earlier screening if available, citing very similar reasons for this choice as the women reported here. However, we were surprised that women still express this clear preference when informed of the high probability that a Down's syndrome pregnancy may miscarry between 10 and 15 weeks of gestation. Approximately 15% of Down's syndrome pregnancies may miscarry between the timing of first and second trimester screening6,7. In addition, ‘screen positive’ affected pregnancies, whether detected by biochemical screening or nuchal translucency, may have a higher spontaneous loss rate10,11. It is therefore not improbable that as many as 1 in 6 of the Down's syndrome pregnancies detected by nuchal translucency or serum screening at 10 to 12 weeks of gestation will miscarry before maternal serum screening at 15 to 16 weeks of gestation6. A justified criticism of first trimester screening12, indeed a criticism that we have made ourselves13, has been that some women will face unnecessary decisions regarding invasive diagnosis and, ultimately, pregnancy termination in an affected pregnancy that would otherwise have ended in a spontaneous miscarriage before serum screening at 15 weeks of gestation. While this criticism remains valid, it appeared irrelevant to the majority of women we questioned. Ninety-one percent of women chose early screening, even if the majority of affected pregnancies identified by this test miscarried before the later screening. Explaining this choice, the women studied would wish to know if their fetus had had Down's syndrome, regardless of the pregnancy outcome, and they also valued the knowledge of an underlying reason for a miscarriage, if it occurred. Unfortunately, some women chose the early test because they interpreted the selective detection of affected pregnancies destined for miscarriage as a diagnostic test for miscarriage. It is possible that this misinterpretation may have exaggerated the preference for first trimester screening.
We also wished to discover whether the implications for the management of subsequent pregnancies conferred by the diagnosis of Down's syndrome in one pregnancy, regardless of the outcome of that index pregnancy, would affect their choice of screening test. Current data on recurrence risk of Down's syndrome are based on live births and pregnancies proceeding well into the second trimester rather than on affected pregnancies detected in the first trimester. Therefore, it would be expected that widespread first trimester screening will eventually result in more women having diagnostic procedures in subsequent pregnancies following a ‘past history’. Interestingly, this information did not affect the decisions of the majority of women in this study. Furthermore, of the six women who stated that this new information would alter their decision, all declared that they would be more, not less, likely to choose early screening tests because of it.
Importantly, the setting in which we investigated the women's attitudes to the various screening tests is similar to the real life clinical situation. In our institution women are offered screening at their first clinic visit, and they usually decide at that visit whether to schedule second trimester screening. Accordingly, we interviewed women at their first antenatal visit and asked them to express their preferences at that time in light of the limitations and implications of the various tests available. We believe that this was an important feature of the study, because with the advent of first trimester screening women will be faced with these choices at their first visit. Much less time for reflection will be afforded by first trimester screening than is current with second trimester screening.
Currently, our hospital is involved in a prospective study assessing the relative merits of first and second trimester screening tests for Down's syndrome. As part of this study, all women receive written information outlining what Down's syndrome is and what prenatal tests are available before they attend for their first hospital visit. It was therefore disappointing that the women still appeared to have little knowledge of either Down's syndrome or the screening and diagnostic tests, although similar findings in women who have had an obstetric consultation have been reported by others14. Nonetheless, the decision to undergo prenatal screening should be made by women only after they have received adequate counselling and information15, and the results of our small study re-emphasise the need for health professionals to ensure that this information has been understood. The apparent difficulty in handling this information, and the new immediacy that first trimester screening brings, demands improved strategies for ensuring that care is appropriate. The need for ensuring that complex information is imparted is further highlighted by a recent suggestion that women who have prenatal testing may be less critical in their decision processes than those who choose not too16.
In summary, we have shown that women who choose to have prenatal screening for Down's syndrome prefer as early testing as possible, irrespective of the likelihood that such testing will detect pregnancies destined to miscarry. These findings would favour the continued development of first trimester screening programmes.