Amniocentesis in the third trimester of pregnancy

BACKGROUND: Amniocentesis in the third trimester, which reduces risks of procedure-related miscarriage but still allows termination of affected fetuses, may be applicable in some pregnancies. The implications of deferring amniocentesis include complications, delivery before the test and increased amniotic fluid culture failure rates. We investigated the indications, complications, karyotype results and laboratory failure rates of third-trimester amniocentesis. METHODS: We studied all women who underwent third-trimester amniocentesis from 2000 to 2006. Data were collected from ultrasound databases, computerised records and individual chart review. RESULTS: We reviewed 165 pregnancies that underwent amniocenteses after 28 weeks. Median maternal age at amniocentesis was 32 years and median gestation, 32(+2) weeks. Indications included malformation (60/165), soft markers (37/165), maternal request (12/165), and positive screening test (11/165). Of the 49 women(29.7%) who declined second-trimester amniocentesis, 24.5% had twins and 38.8%, malformations. Amniocentesis was not offered to 116 women: 57/116 (49.1%) third-trimester referrals, 25/116 (21.5%) diagnosed late and the remainder, low-risk indications. Fetal karyotype was abnormal in 17 cases (10.3%). Seven women who initially declined amniocentesis had abnormal results compared with one advised to have late amniocentesis. Culture failure rate was 9.7%, however results were obtained by Quantitative fluorescent polymerase chain reaction (QF-PCR) from 164/165 samples. Complication rate was 1.2%. CONCLUSION: For late diagnoses and for low-risk indications, third-trimester amniocentesis is an acceptable option, especially when utilising QF-PCR with cytogenetic culture.     

The Role of the Nurse During Amniocentesis

Amniocentesis is a relatively simple, safe, and accurate diagnostic tool which is being performed with increased frequency in local hospitals. The maternity nurse has a responsibility to know the clinical applications, the role of the nurse during the procedure, and the potential risks associated with amniocentesis.     

An Evaluation of Early Amniocentesis

Early amniocentesis (EA) for prenatal diagnosis at less than 14 weeks gestation is becoming more common. The number of randomized studies are small and have not had the power to determine the accuracy and safety of the procedure when compared to chorionic villus sampling or mid-trimester amniocentesis. Procedures at 11+0 to 12+6 weeks should be considered experimental. This review discusses the ethics, embryology, and clinical experience in obtaining samples for cytogenetics, amniotic fluid alpha fetoprotein (AFP), and acetylcholinesterate (AChE) estimation. The procedure and cytogenetic failures, spontaneous and therapeutic pregnancy losses, and congenital anomalies associated with early amniocentesis will be described.     

Amniocentesis and the management of premature labor

Two applications of amniocentesis for the evaluation of the patient in idiopathic premature labor, fetal lung maturity testing, and detection of occult intraamniotic infection were evaluated in a review of 59 cases. Seven patients (12%) had positive amniotic fluid cultures despite the absence of clinical signs of infection. This group presented at earlier gestational ages (29 + 2.3 versus 32 + 2.0 weeks, P less than .005) and were more likely to rupture membranes while on tocolytic therapy (four of seven versus two of 52, P less than .001) than patients whose cultures were negative. All seven patients with a positive culture delivered within 48 hours of admission, whereas 44 of 52 patients with negative cultures delivered after 48 hours (P less than .001). Increase in maternal and neonatal morbidity seemed to be related primarily to a higher cesarean section rate and earlier gestational ages at delivery in this group. Lecithin/sphingomyelin ratio was predictive of fetal lung maturity as expected. More than one-half of patients greater than 33 weeks and one-third of patients at 31 to 32 weeks demonstrated fetal lung maturity. The authors conclude that amniocentesis is an important tool in evaluating patients in preterm labor, especially with respect to making appropriate management decisions regarding tocolytic and/or corticosteroid therapy.     

Amniocentesis and Its Complications

This study was conducted in order to evaluate whether the performance of an experienced operator had any significant influence in reducing the incidence of complications in amniocentesis; 1,459 women had amniocentesis performed under ultrasound guidance; 1,324 were performed by experienced operators and 135 cases by less experienced operators. Complications like fetal loss, blood-stained amniotic fluid, culture failure, multiple needle puncture, leaking liquor, fetal trauma and error in results were compared in the 2 groups. This study demonstrated that amniocentesis performed by an experienced operator decreased the various complications associated with amniocentesis.     

Amniocentesis and chorionic villus sampling

Amniocentesis and chorionic villus sampling (CVS) remain the most commonly used invasive prenatal diagnostic procedures. Recent reports on early amniocentesis demonstrate its application to the prenatal detection of certain biochemical disorders. However, its role in the evaluation of open fetal defects of the neural tube or ventral wall is still under investigation. The fact that many reports concerning early amniocentesis include a majority of patients beyond 11 to 12 weeks' gestation, thus placing the procedure outside the first trimester, make comparisons with CVS (usually performed between 9 and 11 weeks) problematic. The role of midtrimester amniocentesis in evaluating elevations of maternal serum alpha-fetoprotein, following a normal ultrasonographic examination performed specifically to detect fetal anomalies, is under scrutiny. It appears that risk adjustment may be appropriate following a normal scan, and prior to invasive procedures, but each center's recommendation to a given patient will depend on the expertise of the individual sonographer, as well as the quality of examination. CVS has gained acceptance as a safe first-trimester means of prenatal diagnosis, with increasing applications in the later stages of pregnancy. Chromosomal mosaicism detected by CVS may represent a phenomenon inherent to placental tissue; questions remain regarding mosaicism as a potential marker for increased pregnancy loss. Comparisons between the transcervical and transabdominal routes are reviewed, with equivalent results regarding safety and efficacy. Recent evaluations of fetomaternal transfusion following CVS are also described.     

Genetic Amniocentesis in Twin Pregnancy

Summary: In a series of 800 referred patients, the diagnosis of 11 twin pregnancies was made by ultrasound prior to genetic amniocentesis. Amniocentesis of both gestation sacs was successful in all 11 patients. Genetic counselling in twin pregnancy should assess precisely the indications, specificity and complications of differential amniocentesis.     

Amniocentesis in twin pregnancies

Objective  To describe the experiences in diagnostic amniocentesis in twin pregnancies. Methods  The computerized database and medical records of pregnant women attending Maternal Fetal Medicine Unit of the hospital for diagnostic amniocentesis at 16–20 weeks gestation between January 1992 and December 2006 were retrospectively reviewed. Results  During 15 years of experience, 7,890 amniocenteses at 16–20 weeks gestation were performed for prenatal diagnosis, including 174 procedures in 87 twin pregnancies. The mean gestational age at the time of amniocentesis was 17.13 ± 3.35 weeks. Preterm birth rate defined as the delivery before 36 gestational weeks was 36.24%. The total fetal loss rate was 5.17%, however, the procedure related fetal loss within 2 weeks after the procedure was 1.15%. Conclusion  Based on our limited data and previous studies, we can counsel patients undergoing twin amniocentesis at mid-trimester that the fetal loss rate may be slightly higher than that of singleton amniocentesis.     

Intraamniotic Bleeding Following Transabdominal Amniocentesis

A prospective study on 231 consecutive patients who underwent transabdominal genetic amniocentesis was performed to determine the incidence of intraamniotic bleeding associated with needle removal and to determine if this increased future pregnancy complications. Eleven procedures traversed the placenta and intraamniotic bleeding was seen in every case. In 220 cases the placenta was not traversed and intraamniotic uterine wall bleeding was seen in 38%. In 92% of these, bleeding stopped in less than 30 sec. No difference in pregnancy outcome was seen between cases with visible bleeding when compared to cases where bleeding was not identified, suggesting that this is a normal but unavoidable aspect of amniocentesis. The location of the placenta was not a factor except that a transplacental procedure was more likely with an anterior placenta. Possible explanations for this unexpected high incidence are discussed as well as the theoretical concern over exposing the unborn fetus to maternal blood borne infections.     

Amniocentesis and chorionic villus sampling

Invasive prenatal diagnosis continues to be the gold standard for pregnancies at increased risk of chromosomal aneuploidy or other genetic disease. Chorionic villus sampling is the procedure of choice for the first trimester. Early amniocentesis has been shown to carry increased risks of pregnancy loss, amniotic fluid leakage and talipes equinovarus. Mid-trimester amniocentesis continues to be the most common form of invasive prenatal diagnosis, with post-procedural loss rates of between 0.5 and 1%. This present review summarizes information on technique risks, looks at new technology applied to invasive prenatal diagnosis testing, and reports on new diagnoses that could be made either by amniocentesis or chorionic villus sampling.     

Amniocentesis: A contemporary review

Amniocentesis is an essential tool in obstetrics. Invasive testing remains the only modality for diagnostic genetic testing and the only way to provide comprehensive testing for chromosomal abnormalities. Despite increasing use of cell free fetal deoxyribonucleic acid (DNA) testing, amniocentesis should still be offered to all women who desire more complete and accurate genetic testing. Counseling patients on the limitations of screening tests is of the upmost importance and amniocentesis should continue to be recommended to confirm positive results from cell free fetal DNA testing or in the case of failed cell free fetal DNA test. As cell free fetal DNA screening has not adequately been studied in multiple gestations, its use is not recommended in this population and invasive testing should be offered. Amniocentesis is also very useful in providing additional information in settings other than genetic testing the second and third trimester. If intraamniotic infection is suspected, but the clinical findings are not enough to guide management, amniocentesis can provide testing that can both immediately clarify the picture (interleukin-6, gram stain, glucose levels) and finally confirm the presence of infection (culture). It can also be used to detect the presence of intrauterine viral infections. Additionally, amniocentesis may be used to test for markers of fetal lung maturity. The American Congress of Obstetricians and Gynecologists recommends that amniocentesis for this indication not be used in cases where late preterm delivery is indicated. It may be useful in guiding decision-making, however, when late preterm delivery is indicated, but when exact timing is unclear. Regardless of the indication, amniocentesis appears to be a relatively low risk procedure with minimal risk to the patient. Additional randomized controlled trials are not likely, as they are not feasible to due extremely high number of participants that would be needed to detect a difference in loss rates. Based on current literature, however, the risk of pregnancy loss from second trimester amniocentesis is low in both singleton and twin gestations. We counsel patients that technique has changed since the original studies in the 1970s and feel comfortable quoting a loss rate of 1/500-1/1000 based on contemporary data.