guidance on antenatal screening

The pregnant woman must understand the condition being screened for. The midwife should explain about the nature, purpose, risks, benefits, timing, limitations and potential consequences of screening.

The woman should understand that screening is optional, and understand the risks and benefits of not undergoing screening. the choice of continuing or terminating a pregnancy for serious fetal abnormalities

Local knowledge should be shared: how, where and when the test is done: What the test results mean and potential significant clinical and emotional consequences. The decisions that might need to be made at each point along the pathway and their consequences. How and when the results will be given.

-Common misunderstandings are that Down syndrome cannot occur if it has not previously occurred in a family or that a woman is too young to have an affected baby. Many women (and their partners) do not understand that syphilis is a sexually transmifed infection, but that the initial result can show positive if there have been similar non-sexually transmitted infections

-Women who decline first trimester screening should know that they can take up second trimester screening for Down's syndrome if they change their mind and that they can undergo second trimester screening for fetal anomaly at 18+0 to 20+6 weeks. - Women who decline initial screening for infections can and should be offered screening later in the pregnancy. Importantly, only the woman has the right to consent to or decline the screening tests. A partner or family member has no right to consent or decline on her behalf. Women can withdraw consent for testing at any time. This decision should be recorded.

The process of consent requires adequate time. to ensure that the woman has had the time she needs has been enough time to ask questions, that she feels comfortable -The amount of information needed will vary between women.

Issues to consider when presenting information understand the motivations and thought processes of pregnant women. The motivation for testing ; Mothers ohen think that fetal anomaly tests such as ultrasound scans are an integral or mandatory part of their antenatal care. They may also be unaware of the reasons for performing the test and this can compound the shock of finding problems or abnormalities. When women are anxious or under stress, they are less able to remember the information provided

Parents may feel vulnerable and less able to ask questions. This may lead to dissatisfaction with the quality of communications with health carers. Since an unborn fetus is something of an enigma to parents, this may increase anxiety and sensitivity -The phenomenon of how parents interpret risk information is not fully understood, although it is clear that personal circumstances, preferences and beliefs are an integral part of this process.

-the midwife begins a consultation by investigating how much the mother knows about the condition being tested for, and what she already knows about the test risks, benefits and the consequences of results. - a mother whose friend or neighbour has a baby with Down syndrome may be sensitized to this possibility and overestimate the chances of it happening to her. -Mothers who work with infirm people, or those with a disability, are most likely to seek prenatal diagnosis

Explaining risk The way in which the midwife tells a mother about risk will also greatly influence how that risk is perceived. For example, a mother who is told that her risk of a particular condition is 1 in 10 may be more alarmed than if she had been informed that there was a 90% chance of normality. or 9 out of 10 babies will not be affected by the condition. This is known as the ‘framing’ effect

People vary considerably in the ways that they consider and understand risk, it is important that this information is presented in a variety of ways using appropriate language. the use of the word ‘chance’ rather than ‘risk’ and that the chance of the outcome (which for antenatal screening now mainly relates to screening for Down syndrome) be given as a percentage as well as a ratio 1 in x. As such, a midwife discussing a 1 in 100 chance of a disorder should also point out the fact that 99% or 99 out of 100 similar people will not experience that disorder.

Ge ne r a l pr inciple s whe n pr o v iding inf o r m a t io n Be clear: explain everything in terms that are not medical or complex – be simple, concise and to the point. Give important information first. Group pieces of information into logical categories, such as treatment, prognosis and ways to cope. Information may be recalled more easily if it has been presented in several forms. For example, leaflets can be helpful.

Offer to answer any queries Offer to answer any queries. Give contact numbers, in case people think of questions at a later date. Do not make assumptions about information requirements on the basis of social class, profession, age or ethnic group. Summarize, check understanding and repeat the information. Ask whether there is anything that remains unclear.

-every woman should have the results of all of their screening tests recorded in their hand-held notes within 14 days or at the 16 week antenatal appointment. a test is not performed or sample not processed because in some way the process failed, this is recognized in a timely enough fashion for the test to be repeated, and that the results are recorded in the woman's hand-held notes.

Individual screening test considerations Antenatal screening tests are broadly divided into those that are looking for a problem in the mother that could affect the fetus, such as an infection, the presence of a red-cell antibody, or a particular haemoglobin variant, which if passed on by both parents could cause an issue, or those looking directly for a problem in the fetus.

Fetal screening tests Population screening of the fetus (i.e. that offered to everyone) is now directed at two areas: defining the risk of a baby having Down syndrome (trisomy 21), and the detection of specific abnormalities.

Screening for Down syndrome Down syndrome is the most common cause of severe learning difficulty in children. In the absence of antenatal screening, around 1 in 700 births would be affected (Kennard et al 1995). While some children with Down syndrome learn literacy skills and lead semi- independent lives, others remain completely dependent. Around one in three of these babies are born with a serious heart defect.

The average life expectancy is about 60 years, although most people develop pathological changes in the brain (associated with Alzheimer's disease) after the age of 40 (Kingston 2002). Screening for Down syndrome has been driven by both health economics and maternal choice. That is not to say, however, that all mothers wish to be screened, or would act to end a pregnancy if they knew they were carrying an affected fetus. Uptake rates for screening vary depending on the population being screened.

Some mothers will chose screening despite knowing that they would not act on a result that gave them a high chance. Interestingly, the single largest factor in deciding whether to take further tests aher a high chance result is the degree of magnitude of the change in risk. In other words, a mother who has a pre-test chance (based on age alone) of 1 in 100 (1%), who has a screening result of 1 in 120 (0.83%) will be less likely to wish to proceed to further testing than a woman who has a pre-test chance of 1 in 1000, who then receives a result of 1 in 120 chance, even though both are at equal risk of giving birth to a baby with Down syndrome.

The national screening programme for Down syndrome in the UK comprises the offer of one of two tests The gestational age window for a combined test starts from 10+0 weeks to 14+1 weeks in pregnancy. The combined test comprises measurement of the crown–rump length (CRL) (Fig. 11.1) to estimate fetal gestational age (dating scan), measurement of the nuchal translucency (NT) space at the back of the fetal neck (Fig. 11.2) and maternal blood to measure the serum markers of pregnancy-associated plasma protein A (PAPP-A) and human chorionic gonadotrophin hormone (hCG).

Using this test, 90% of fetuses affected with Down syndrome would be expected to fall into the high-chance category (a chance of 1 in 150 or more) (the detection rate) with 2% of women carrying unaffected babies having a chance of 1 in 150 or higher (a screen positive rate of 2%). The quadruple test window starts from 14+2 weeks to 20+0 weeks. A maternal blood sample is required for the analysis of hCG, alpha-fetoprotein (aFP), unconjugated oestriol (uE3) and inhibin-A.