Farzad Mehrnaz MD

INTRODUCTION

Twenty years after mid-trimester genetic amniocentesis-, first trimester invasive prenatal procedures were introduced, and many centers began to look into an alternative for first trimester diagnosis (1). Chorionic villous sampling is an alternative for earlier prenatal diagnosis. Early amniocentesis (EA) can be performed effectively, as shown over the years in many observational studies and partially randomized and randomized trials, but, a multicenter randomized trial (Canadian Early and Mid-trimester Amniocentesis Trial) reported a higher total pregnancy loss, a significant increased incidence of musculoskeletal foot deformities, a significant increased culture failure rate, and an increased post amniocentesis rate of leakage in the EA group compared with mid-trimester amniocentesis⁽¹⁾. Recently the biochemical blood test of free b-hCG (beta human chorionic gonadotropin) and PAPP-A (pregnancy associated plasma protein A) and the measurement of nuchal translucency have reduced the need for invasive prenatal diagnosis at first trimester⁽²⁾ but some abnormal answers, on rechecking data have failed to detect some abnormality like thalassemia, justifying the performance of chorionic villous sampling. Termination of abnormal fetuses in Iran is prohibited after 16 weeks of pregnancy and any prenatal diagnosis must be proved up to this date. Chorionic villous sampling is done at limited centers and our clinic is one of the referral clinics for these procedures, including CVS and amniocentesis which are performed by one expert obstetrician in this field.

We did a prospective study of women with singleton viable pregnancies who were referred for first-trimester fetal karyotyping because of advanced maternal age, parental anxiety, or family history of genetic or chromosomal abnormality by trans-abdominal CVS during the years of 2005-7. Gestational ages were proved after 9 weeks of conception by ultrasounds that reconfirmedthem. Half of an hour before the procedure they took a 500mg capsule of Cephalexine and one tablet of acetaminophen-. Procedure was done by insertion of an 18-gauge needle by transabdominal-guided ultrasound (Honda2000, convex probe) needle (number18, GTA, 20 centimeter). The participants in our study were one thousand pregnant women. The procedure-related pregnancy loss rate was obtained up to more than two and less than four weeks after the procedure from total pregnancy losses. We followed the cases up to one year after procedure. All the procedures were done by just one physician and one basis for procedure. Technique was aspiration and fine suction of chorionic villous preferably by one sampling but it could be repeated after failure of the first attempt. The samples were collected in sterile physiologic serum and forwarded to the standard genetic laboratory. Data were collected and analyzed by descriptive statistics.

CVS was performed for 1,000 referred cases. They requested CVS due to: familial history of thalassemia; both parents have beta-thalassemia trait (77%), detection of fetal sex (8.4%), diagnosis of systemic muscular atrophy (SMA)(4.4%), sickle cell anemia,(1.7%), hemophilia (1.6%) and Duchene disease (1.6%).

Mean age of women was 26.7±5.3 (15-43 year). Approximately 38.5% were nulliparous (Table 1.). Mean gestational age was 11.4±1.7 (9-21) weeks. The placental site as shown in Table 2 is mostly at the posterior wall of the uterus. Sampling was successful in all cases. Attempt to achieve chorionic villous was by one needle at 71.1%, two at 23.1%, three at 4.9%, four attempts at 0.8% and six at 0.1%. The needle crossed the amniotic sac in 58 cases (5.8%).

Among one thousand procedures, one case had rupture of amniotic sac three days later and fetal loss (0.1%) following that. Most of the cases (849) were followed for one year, except 151 women who were not available. Among samples, one case had congenital heart disease and one intrauterine death near term and another had preterm pregnancy. All other cases were apparently healthy infants and the results of their genetic studies have been recorded.

Systematic reviews imply the risk of fetal loss attributed to invasive prenatal procedures by a range of 0.6-2%. Estimate of pooled pregnancy loss within 14 days has been 0.6% rising to 0.9% for pregnancy loss before 24 weeks and 1.9% for total pregnancy loss. Corresponding figures for CVS were 0.7%, 1.3%, and 2%⁽³⁾. The data on multiple insertions showed large heterogeneity, ranging from 0.2% to 2.9% for amniocentesis (pooled risk 2.0% and from 1.4% to 26.6% for CVS (pooled risk 7.8%). Only five amniocentesis studies provided controls, but none was matched for gestational age. Pooled relative risks for fetal loss before 28 weeks and total pregnancy loss were 1.46 and 1.25, respectively⁽³⁾. However mid trimester amniocentesis is an easy performed procedure compared to CVS but a major disadvantage of amniocentesis is that the result is usually available only after 16-18 weeks' gestation. Chorionic villous sampling (CVS) and early amniocentesis can be done between 9 and 14 weeks and offers an earlier alternative⁽⁴⁾ However, second trimester amniocentesis is safer than trans-cervical CVS and early amniocentesis. If earlier diagnosis is required, transabdominal CVS is preferable to early amniocentesis or transcervical CVS. In circumstances where transabdominal CVS may be technically difficult, the preferred options are transcervical CVS in the first trimester or second trimester amniocentesis⁽⁴⁾. Several cohort studies have shown the feasibility of early amniocentesis (between 11 and 13 weeks of gestation) as an alternative to chorionic villus sampling (CVS) for karyotyping, but the only completed randomised study of fetal safety showed a significant fetal-loss risk related to first-trimester amniocentesis and even though the numbers were small, they found an association between early amniocentesis and talipes equinovarus (1.63) that was higher than in the CVS group (0.56%), but this difference was not significant^(5,6). Our study showed just 0.1% risk of fetal loss. We conclude that chorionic villus sampling is a safe and effective technique for the early prenatal diagnosis of cytogenetic abnormalities.

One of the upcoming non-invasive techniques of prenatal diagnosis is maternal blood sampling for fetal blood cells in which the fetal cells for particular DNA sequences can be sorted out and analyzed by a variety of techniques, but without the risks that invasive procedures inherently have.

Fluorescence in-situ hybridization (FISH) is one technique that can be applied to identify particular chromosomes of the fetal cells recovered from maternal blood, and diagnose aneuploid conditions such as the trisomies and monosomy X⁽⁷⁾. The request of our patients are mostly for detection of or or to rule out thalassemia and the problem with this technique is that it is difficult to get many fetal blood cells. There may not be enough to reliably determine anomalies of the fetal karyotype or assay for other abnormalities. Although the risk of pregnancy loss is relatively low, lack of adequate controls tends to underestimate the true added risk of prenatal invasive procedures. We conclude that chorionic villous sampling is a safe and effective technique for the early prenatal diagnosis of cytogenetic abnormalities but that it probably entails a slight risk of procedure failure and of fetal loss that can be controlled by skill improvement.

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6. prenatal diagnosis:
   http://library.med.utah.edu/WebPath/TUTORIAL/PRENATAL/PRENATAL.html;