First-trimester scan detects anomalies earlier, but may also have a downside
LUMC
What do expectant parents think of the first-trimester scan, and how reliable are the results? PhD candidates Kim Bronsgeest (LUMC) and Eline Lust (UMC Utrecht) investigated these questions in the IMITAS study, which will help decide whether the scan is introduced permanently.
Since 2021, expectant parents have been able to choose whether to have a first-trimester scan. This scan can detect serious physical anomalies that would otherwise only become visible at the 20-week scan, giving parents more time for further tests and to decide how to respond to the results. On the other hand, an early scan can also cause additional worry and uncertainty. The IMITAS study – which includes everyone who has a first-trimester scan – is investigating whether the benefits outweigh the drawbacks.
Detecting serious physical anomalies
The first-trimester scan focuses on a limited number of serious conditions. It allows doctors to inform expectant parents about any conditions and their prognosis. However, a sonographer may also spot other anomalies. As a result, more anomalies are detected earlier in pregnancy, giving expectant parents more information about their unborn child. ‘But sometimes it takes longer to reach a diagnosis and a clear prognosis’, says Bronsgeest.
How reliable is the first-trimester scan?
Bronsgeest and Lust examined how effectively the scan detects serious anomalies and how often it wrongly suggests one. They analysed data from almost 130,000 pregnant women who took part in the study between 2021 and 2022. These were women with a low risk of having a child with a congenital anomaly. Women with an increased risk – for example, because of specific congenital anomalies of their own – are referred straight to hospital for scans.
The study shows that when the first-trimester scan detects no anomalies, there is still a 1% chance that a mild or serious anomaly will be found at the 20-week scan.
In total, 1.3% of participants were told a possible anomaly had been found and were referred to hospital for a more detailed scan. Half of them were later told that everything was fine after all. The other half underwent further tests, which sometimes led to a diagnosis and sometimes confirmed that the child was healthy. ‘The vast majority of women – around 98% – receive a normal result and can be reassured’, says Bronsgeest. ‘And when an anomaly is present, the scan is extremely valuable because it quickly clarifies the diagnosis and what it means for their unborn child.’
Psychological impact on expectant parents
In addition to studying the scan’s technical performance, the two PhD candidates also examined its psychological impact on expectant parents through interviews and questionnaires. ‘We looked at the impact of ending a pregnancy at 15 weeks compared with 22 weeks’, Bronsgeest explains. ‘This is always an extremely difficult experience, often involving anxiety, stress and depression symptoms. It turns out that these symptoms are, on average, less severe when the pregnancy is ended earlier. This makes the first-trimester scan hugely valuable for these women and their partners.’
The study also shows that an abnormal result is associated with considerable psychological strain compared with a normal result. This strain appears to be greater for expectant parents who receive an abnormal result at 13 weeks than for those who receive one at 20 weeks. This may be because, at the time of completing the questionnaire, all the women who had received an abnormal result from the first-trimester scan had not yet received a clear diagnosis, which creates uncertainty.
To introduce permanently or not
The results of the IMITAS study are now with the Health Council of the Netherlands, which will advise the House of Representatives on the future of the first-trimester scan. The House of Representatives will ultimately decide whether to introduce the scan permanently.
According to Lust and Bronsgeest, it is not a simple decision. Being able to decide earlier to end a pregnancy benefits some people, and a large group is reassured after learning that everything is fine with their unborn child. But there is also a group that experiences a downside to the scan: they are told something might be wrong, only to later learn that it is not. This is a common consequence of screening in general, and it affects the experience of pregnancy. ‘The screening offers important benefits, and it is up to the Health Council to weigh these against the drawbacks’, says Bronsgeest. ‘I’m very curious to see what they advise.’
Kim Bronsgeest will defend her dissertation on 1 September, from 16.00 to 17.00 hrs, at the Academy Building in Leiden.