Ultrasound defining the fetus as a patient

Advanced technology has enabled a thorough fetal assessment, as David Churchill explains

Developments in fetal medicine are having a profound effect on how pregnancies are managed and have resulted in the fetus becoming a fully fledged patient in its own right. These developments for obstetricians and specialists in fetal medicine will have potentially great benefits in the long term, largely thanks to improvements in ultrasound imaging, which enable obstetricians to diagnose structural and functional abnormalities in the fetus more accurately.

Two dimensional ultrasound imaging is the mainstay of obstetric practice in the United Kingdom. Most pregnant women are offered, and receive, two ultrasound scans as a matter of routine. The first is carried out in the first trimester, with the principal aim of dating the pregnancy accurately. The second is carried out around 20 weeks and is designed to examine the fetus for structural anomalies. In recent times, the role of ultrasound has extended into diagnosing functional abnormalities and assessing the risk for such complications as preterm delivery, pre-eclampsia, and growth restriction.^{w1 w2}

Detection rates for abnormalities have risen steadily, and most units would now expect to identify a large number of the major structural abnormalities, such as spina bifida, abdominal wall defects (exomphalos), skeletal dysplasias etc.^w3 Skilled practitioners using the best equipment can now identify and delineate structural defects in the fetus from as early as 12 weeks, and many specialists now think that scanning for anomalies can be brought forward in pregnancy.^w4 Some abnormalities, however, cannot be detected until 20 weeks, and currently the second trimester scan therefore remains in the scanning regimes of maternity units.

Three dimensional and four dimensional (real time three dimensional) imaging is creating a further step change. Parents can now see their babies in a more photographically accurate representation, and in some situations this is helping them to more fully understand some abnormalities, such as cleft lip and palate. By providing parents with images that they can understand, doctors can give them more meaningful information. This removes some of the fear for the future.

Ultrasound has also enabled obstetricians to study fetal behaviour and physiology. They now have a greater understanding of how the fetus responds when subjected to certain disease processes, the most common being placental failure resulting from placental ischaemia and infarction.

The biophysical profile was the first method developed to assess fetal wellbeing. It consists of five variables: gross fetal body movements, fetal tone, fetal breathing movements, liquor volume, and an assessment of the fetal heart rate using cardiotocography. These are combined into a scoring system; zero for abnormal reading and two for normality. A fetus subjected to hypoxia stops moving, loses tone, stops breathing, and reduces renal blood flow, resulting in a reduction in liquor volume. These features would produce a low biophysical profile score.^w5 Many observational data have been produced to support the use of the technique. However, because of a lack of randomised trial data, the technique has now been largely superseded by Doppler ultrasound.

Doppler ultrasound is used to observe the pathophysiological response of the fetus to hypoxia. A fetus in an hypoxic environment invokes certain survival responses. It shunts blood away from the non-essential organs to the vital organs, the brain, heart, and adrenals. By observing the relative increases and decreases in regional blood flow, the delivery of the baby can be timed with greater precision, saving it from morbidity and mortality. On the other hand, the reassurance from normal Doppler findings allows time for the administration of steroids to mature the lungs of preterm babies before the delivery. It is also useful in other conditions. For the same reasons, shunting of blood to the vital organs occurs with fetal anaemia. Measuring blood flow in the middle cerebral arteries has enabled obstetricians to accurately diagnose anaemia before fetal hydrops develops.^w6 Before this discovery, the diagnosis required hazardous interventions such as amniocentesis or fetal blood sampling. Middle cerebral artery Doppler can be applied regardless of the cause of the anaemia and after the diagnosis, treatments can be administered. In some cases this may entail a blood transfusion in utero. For patients with twin to twin transfusion syndrome in addition to blood transfusions, it is possible between 16 and 26 weeks to carry out laser ablation of the arterovenous anastomoses causing the loss of blood from one fetus to the other, thus halting the progress of the disease.^w7 This technique has led to dramatic improvements in outcome for this very high risk condition.

The benefits of improved ultrasound imaging are an increasing number of fetal therapies, and the pioneers are still testing the boundaries. Cardiac arrhythmias are being defined and treated with digoxin or flecanide. Some diaphragmatic hernias are now being treated by tracheal occlusion. This raises the pressure in the fetal chest, by preventing escape of fluid from the lungs and helps to push the hernia back into the abdomen. Obstructed bladders and pleural effusions are being drained or shunted with pigtail catheters, and stenotic valves are being balloon dilated in utero.^{w8 w9} Most heroically, open surgery is now being attempted for some fetuses with spina bifida. These techniques are still limited to regional and supraregional centres, but they show how far thinking has progressed.

This optimism must, however, be tempered with some caution. Research shows that some techniques carry a high price in mortality and morbidity. For example, vesico-amniotic shunts can migrate intra-abdominally, causing urinary ascites, and overall the death rate for pregnancies that have undergone shunting is in the order of 60%.^w10 However, it is not inconceivable that further developments enabling a greater understanding of these disease processes will result in further advances in the areas of fetal imaging and therapy.

Any interaction between doctor patient starts with observation. Ultrasound enables obstetricians to observe the fetus and its behaviour in detail, expanding the horizon of possibilities for diagnosis and treatment. It is said, unfairly, that fetal scanning is a "search and destroy” mission. Such a statement should be confined to the dustbin. Our understanding of fetal structure and life in utero is increasing exponentially. The variety of investigations and treatments now available mean that a baby is no longer a by-product of pregnancy, but an integral part of the duo and in some instances a patient in its own right.

Competing interests: None declared.

1. Honest H, Bachmann LM, Coomarasamy A; et al. Accuracy of cervical transvaginal sonography in predicting preterm birth: A systematic review. Ultrasound Obstet Gynecol 2003; 22: 305-322.
2. S Campbell. First-trimester screening for pre-eclampsia. Ultrasound Obstet Gynecol 2005; 26: 487 – 489
3. E Garne, M Loane, H Dolk, C De Vigan, G Scarano, D Tucker, C Stoll, B Gener, A Pierini, V Nelen, C Rosch, Y Gillerot, M Feijoo, R Tincheva, A Queisser-Luft, M C Addor, C Mosquera, M Gatt, I Barisic. Prenatal diagnosis of severe structural congenital malformations in Europe. Ultrasound Obstet Gynecol 2005; 25: 6 – 11
4. Economides DL, Whitlow BJ, Braithwaite JM: Ultrasonography in the detection of fetal anomalies in early pregnancy. BJOG 1999; 106: 516-523.
5. Manning FA, Snijders R, Harmann CR, et al. Fetal biophysical profile score:VI. Correlation with umbilical artery venous pH. Am J Obstet Gynecol 1993; 169: 755-763.
6. G Mari Middle cerebral artery peak systolic velocity for the diagnosis of fetal anaemia: the untold story. Ultrasound Obstet Gynecol 2005; 25: 323 – 330
7. Senat MV, Deprest J, Boulram M, et al. A randomised trial of endoscopic laser surgery versus serial amnio-reduction for severe twin-to-twin transfusion syndrome at midgestation. N Engl J Med 2004; 35: 136-144.
8. R P Smith, S Illanes, M L Denbow, P W Soothill. Outcome of fetal pleural effusions treated by thoracoamniotic shunting Ultrasound Obstet Gynecol 2005; 26: 63 – 66
9. L E Wilkins-Haug, C B Benson, W Tworetzky, A C Marshall, R W Jennings, J E Locks. In-utero intervention for hypoplastic left heart syndrome – a perinatologist’s perspective. Ultrasound Obstet Gynecol 2005; 26: 481 - 486
10. TJ Clark, WL Martin, TG Divakaran, et al. Prenatal Bladder drainage in the management of fetal lower urinary tract obstruction: A systematic review and meta-analysis. Obstet Gynecol 2003; 102(2):367-382

   

           

	EDITORIALS Ultrasound defining the fetus as a patient       David Churchill (March 2006)
	Rahul Potluri (March 29th, 2006)       3rd Year Medical Student , University of Birmingham rxp289@bham.ac.uk
	It was extremely interesting to read about the advances in technology leading to better understanding of our knowledge of the fetus as a patient. Also addressing the fetus as a patient rather than a "by-product of pregnancy" is innovative and will broaden future treatment approaches. However, ethical issues may play their part in such a move. More specifically, the improving technology has meant that the visualisation of a fetus is now possible well before the maximum abortion limit of 24 weeks in the UK. Given the emotional and moral issues surrounding the topic, it could be possible for the maximum time limit for abortion could be lowered. European countries such as Germany, Spain and Russia already have maximum time limits of 22 weeks. In fact there has already been some activity in this regard, with the House of Commons setting up a joint committee in March 2005 to consider the scientific, medical and social changes in relation to abortion, an issue that has not been considered in the past 16 years. A change in the law may be imminent in view of the technological advances and change has to be the way in modernising medical practice for the better. However, some very difficult emotional, moral and ethical issues will arise. Respect must be shown to these factors before contemplating a change in medical practice, given their sensitive nature.