Dr Kypros H. Nicolaides doesn't mince any words when it comes to what's right and wrong in fetal medicine. As director of Harrisburg Birthright Centre for Fetal Medicine and founder of the Fetal Medicine Foundation in London, Kypros has extensive experience in fetal medicine and over 500 research papers and 30 books to his credit.
He recently shared his knowledge with delegates at the Ninth South Asian Clinical UltraSonography in Practice (CUSP 2004) conference through a live video presentation. The focus was using ultrasound to identify the high-risk group for fetal abnormality, impaired placenta, and preterm delivery -- all three are major causes for pregnancy-related death.
Traditionally an ultrasound scan is done between 15-20 weeks, but advances in imaging technology have made it possible to now do scans between 11-14 weeks.
To detect the risk of cardiac defects in the fetus, uterine artery Doppler ultrasound is used to arrive at the uterine artery pulsability index. The higher the pulsability, the greater the risk of pre-eclampsia.
Nearly 80% of cases that develop pre-eclampsia have high pulsability. So, Nicolaides concluded, the accurate way to assess the pre-eclampsia risk was to measure the risk from uterine artery pulsability in addition to the maternal factors affecting it (Best Practice & Research: Clinical Obstetrics & Gynaecology, June 2004, Vol. 18:3, pp. 383-396).
Cervical sutures
The risk of preterm delivery, also a leading cause of death, is identified by measuring the cervical length at 22 weeks. A multicentre study involving 40,000 women found that the shorter the cervix, the higher the risk. The normal length of the cervix is 37 mm. The risk is high especially if the cervical length is below 25 mm, and even higher if it is below 15 mm.
Cervical length is the key parameter to determine pre-eclampsia risk, and 70% of women can be identified through it. Body mass index (BMI) also has an impact, though, with both higher and lower BMI being risky.
Cervical sutures, long thought of as the best solution for preterm delivery, do not in fact significantly prevent it. Rather, it is the less-expensive treatment with progesterone that is more effective (American Journal of Obstetrics and Gynecology, February 2003, Vol. 188:2, pp. 419-424). "One pessary every night can halve the risk, and in severe cases by over 80%," Nicolaides said.
CVS versus amniocentisis
When it comes to invasive testing for chromosomal abnormalities, Nicolaides favours chorionic villus sampling (CVS) to amniocentesis. Both procedures have high operative risks if they are done without adequate training, which constitutes a minimum of 100 procedures done under direct supervision, according to Nicolaides.
Amniocentesis should never be done before 15-16 weeks, and CVS should not be done before 11 weeks.
The inherent risks in amniocentesis are that a blood vessel can be punctured accidentally, causing the fetus to bleed to death. Other risks include bacteria entering the uterus and ruptured membranes. In CVS, on the other hand, the inherent risks are puncturing the chorionic plate and introducing bacteria. So in comparison, the inherent risk of miscarriage is lower with CVS than with amniocentesis.
Secondly, there is a better possibility of the bacteria being destroyed if they are introduced in the villous space that is rich in white blood cells, rather than in the amniotic cavity, where they can multiply easily. "So at least theoretically, it will be much safer to do a CVS," Nicolaides said.
CVS can also detect mosaic placenta, leading to further investigations on whether the fetus is normal or abnormal, and possibly to a diagnosis of uniparental disomy in certain cases. In other words, it gives more information for correct, subsequent management of the condition.
For both amniocentesis and CVS, no matter whether the placenta is anterior or posterior, Nicolaides advised that the uterus has to be entered laterally so a greater length of the placenta can be sampled.
Once a sample is obtained, should it be analysed using new molecular biology techniques or traditional karyotyping? Molecular biology techniques are less expensive and require a maximum of two days and a minimum of a couple of hours, as opposed to the 15 days karyotyping requires. Molecular biology can also effectively diagnose most abnormalities, including trisomy 18 and trisomy 21. Only a small proportion of cases with chromosomal rearrangements cannot be detected with it. And in reality, screening is done only for major chromosomal abnormalities, Nicolaides said.
Molecular biology versus karyotype is currently one of the much-debated issues in fetal medicine.
By N. Shivapriya
AuntminnieIndia.com staff writer
October 6, 2004
Related Reading
Biochem enters ultrasound domain in fetal screening, October 1, 2004
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