he volume of fluid generally needed for commonly performed analyses is shown in Table 14-12. Because the initial 1 to 2 mL of fluid aspirate may be contaminated with maternal cells, it is generally discarded. Approximately 20 to 30 mL of fluid is then collected for either fetal CMA or karyotyping before removing the needle. Sonography is used to observe the uterine puncture site for bleeding, and fetal cardiac motion is documented at the procedure's end. If the patient is h D-negative and unsensitized, anti-D immune globulin is administered following the procedure (Chap. 15, p. 305).
Multifetal Pregnancy. When performing the procedure in a diamnionic twin gestation, careful attention is paid to the aThe volume of fluid needed for each test may vary according to individual laboratory specifications.
bFluorescence in-situ (FISH) is typically performed for chromosomes 21, 18, 13, X, and Y.
PCR = polymerase chain reaction.
location of each sac and the dividing membrane. Until recently, a small quantity of dilute indigo carmine dye was often injected before removing the needle from the irst sac, with return of clear amnionic fluid anticipated following needle placement into the second sac. Because of widespread shortages of indigo carmine dye, most experienced providers ofer amniocentesis in multifetal gestations when indicated, without dye injection. Methylene blue dye is contraindicated because it has been associated with jejunal atresia and neonatal methemoglobinemia (Cowett, 1976; van der Pol, 1992).
he procedure-related loss rate following midtrimester amniocentesis has decreased with improvements in imaging technology. Based on single-center studies and metaanalysis data, the amniocentesis procedure-related loss rate approximates 0.1 to 0.3 percent when performed by an experienced providerabout 1 per 500 procedures (Akolekar, 2015; American College of Obstetricians and Gynecologists, 2016b; Odibo, 2008). he loss rate may be doubled in women with class 3 obesity, which is a body mass index (BMI) >40 kg/m2 (Harper, 2012). In twin pregnancies, Cahill and coworkers (2009) reported a loss rate of 1.8 percent attributable to amniocentesis.
he amniocentesis indication can influence loss rates, which can be greater with some fetal abnormalities, aneuploidies, and conditions such as hydrops. nd, some losses are due to abnor mal placental implantation or abruption, uterine abnormalities, or infection. Wenstrom and colleagues (1990) analyzed 66 fetal deaths following nearly 12,000 procedures and found that 12 per cent were associated with preexisting intrauterine infection.
Other complications of amniocentesis include amnionic fluid leakage or transient vaginal spotting in 1 to 2 percent. Following leakage of amnionic luid, which generally occurs within 48 hours of the procedure, fetal survival exceeds 90 percent (Borgida, 2000). Needle injuries to the fetus are rare. Amnionic fluid culture is successul in more than 99 percent of cases, although cells are less likely to grow if the fetus is abnormal (Persutte, 1995).
This describes amniocentesis performed between 11 and 14 weeks' gestation. he technique is the same as for traditional amniocentesis, but sac puncture may be more challenging due to lack of membrane fusion to the uterine wall. Less luid is typically withdrawn-approximately 1 mL for each gestational week (Shulman, 1994; Sundberg, 1997).