We obtained clear amniotic fluid in 490 (87%) of the procedures, bloody fluid in 55 (10%), and meconium-stained fluid in eight (1.4%). The color of the fluid was not recorded for four (0.7%) of the amniocenteses, and no fluid was obtained in the five unsuccessful attempts. The incidence of bloody amniotic fluid was higher if more than one needle stick was necessary (30% versus 8%, P = .001) or if the needle traversed the placenta (40% versus 3.6%, P = .001).
There were a total of four complications for a rate of 0.71% (95% CI 0.2%, 1.9%). Table 3 contains the details of these cases. All of the mothers and infants had a good outcome, and none had an emergency cesarean delivery. All four amniocenteses with complications were performed by senior level residents (PGY 3 and 4) with a single needle stick. We were unable to demonstrate a significant difference in the complication rates between resident and staff/fellow physicians (0.93% versus 0, P = .58) or in the presence of clear versus bloody amniotic fluid (0.41% versus 1.8%, P = .27). We could not determine whether the complications were associated with oligohydramnios or traversing the placenta because this information was not recorded for three of the four cases with complications. In cases 1 and 2, the amniotic fluid leakage and the preterm labor both occurred within 24 hours of the amniocentesis. The complications in cases 3 and 4 were first suspected due to the difficulty in obtaining the amniotic fluid and later confirmed to be due to a finding of abnormal fetal heart rate tracings immediately after the performance of the procedure.
No perinatal deaths or emergent cesarean deliveries for nonreassuring fetal heart rates occurred within 48 hours of amniocentesis (0, 95% CI 0, 0.8%). Among 468 cases with information regarding pregnancy outcomes beyond 48 hours, no patients experienced complications of the amniocentesis.
Before the use of ultrasonography, the risks of third-trimester amniocentesis were unacceptably high (0.4–10.8%) and included fetal injury, fetal death, and even, though rare, maternal death.3
Piiroinen and colleagues reported a 1.8% incidence of premature rupture of membranes, but no serious complications among 501 third-trimester amniocenteses performed immediately after ultrasound examination (but without the use of continuous real time guidance).7
Most obstetricians now perform amniocenteses with continuous ultrasound guidance. We preformed a medical literature search using OVID from the years 1970 to 2001 using the search term “amniocentesis” and could locate only two series documenting the risks of a third-trimester amniocentesis with continuous ultrasound guidance.4,5 Haeusler and colleagues reported no complications within 48 hours of an ultrasound-guided amniocentesis among 194 women with gestational diabetes between 24 and 35 weeks' gestation.5 Among 962 third-trimester procedures reported by Stark and coauthors, six (0.7%) required urgent delivery.4 In the latter study, staff obstetricians performed all of the procedures with continuous ultrasound guidance by an experienced sonographer. Although residents performed the majority of amniocenteses in our series, the complication rate was similar to that noted by Stark and colleagues. More importantly, no authors have reported a fetal death due to third-trimester amniocentesis when the procedure has been performed with continuous ultrasound guidance.
No patient in the current series required an emergency cesarean delivery (0, 95% CI 0, 0.8%) immediately after the amniocentesis. Significantly, of the four procedures with complications, all became apparent during the period of monitoring and observation immediately after the amniocentesis. In the series described by Stark and colleagues, six women (0.7%, 95% CI 0.16, 1.24) required an urgent delivery before completion of fetal maturity studies.4 Five of these required emergency cesarean delivery either for fetal heart rate abnormalities (n = 3), placental bleeding (n = 1), abruptio placentae (n = 1), or uterine rupture (n = 1). Although our data suggest that performance of a third-trimester amniocentesis may be safe in a setting where immediate delivery is not available, we still urge caution. Both studies describe complications with the potential to require an immediate delivery. Unfortunately, neither study identifies factors that could be used to determine which pregnancies are at higher risk for such complications.
Both our success rate (99.2%) and that of Stark and colleagues (98.4%), are higher than that reported by Piiroinen and coauthors (87%), where the amniocentesis was done without continuous ultrasound guidance.5,7 This suggests that continuous ultrasound guidance may improve the success rate of third-trimester amniocentesis. Continuous ultrasound guidance may also reduce the number of needle sticks needed for a successful amniocentesis. The average number of needle sticks in our study was 1.1 per patient, which compares favorably to the rate of 1.4–1.6 reported before the use of continuous ultrasound.7–9
Resident obstetricians performed the majority of procedures in the current series, but always with the supervision of staff or fellows. Our complication rate and rate of fetal loss was unaffected by the level of experience of the person performing the amniocentesis, but the power of this study to detect a significant difference is low. The level of experience also did not affect the number of attempts necessary for a successful amniocentesis or the incidence of a bloody tap. Our study gave us a 52% power to detect a significant difference in the need to perform more than one attempt when comparing staff/ fellows versus residents. We recognize the potential for confounding factors in this finding because more complicated amniocenteses were possibly performed by more senior level operators, and the amount of direct supervision of residents was difficult to discern. This low complication rate and high success rate may not apply to an operator without special expertise who performs the procedure without supervision from more highly trained physicians. However, unlike genetic amniocenteses for which complication rates are associated with the level of experience of the operator,10,11 our study suggests that special expertise in third-trimester amniocenteses may not be necessary, but additional studies are needed to confirm this finding. Although this is the second largest study to examine the risk of third-trimester amniocentesis, a much larger study would be needed to better define the risk factors due to the very low complication rate. For example, to achieve a power of 80% to detect a 50% decrease in the complication rate from those procedures performed by residents versus those performed by staff/ fellows or between the risks associated with clear or bloody amniotic fluid, we would need 4,000 subjects in each group. It is unlikely that such a study could be performed in a single institution.
As expected, the incidence of a bloody tap was significantly higher if the procedure required a second pass or if the needle traversed the placenta. The amniocenteses that resulted in a bloody tap, however, did not have a higher complication rate although, again, the power to detect a difference is low. We were unable to determine whether traversing the placenta resulted in a higher complication rate because this information was not recorded for three of the four patients with complications. Stark and colleagues noted that half of their patients with complications had required a transplacental amniocentesis.4 Consequently, we recommend avoiding the placenta when possible. If this is not possible one should take care to minimize lateral movements of the needle and avoid obvious overlying fetal vessels by passing the needle through the placenta at a site distant to the umbilical cord insertion.
In summary, our study demonstrates that third-trimester amniocentesis with continuous ultrasound guidance is safe and almost always successful. Obstetricians may use this information to counsel women regarding the risks and benefits of assessing fetal pulmonary maturity status with amniocentesis in the third trimester. Finally, the small but recognized risk of immediate complications supports a period of observation and fetal monitoring after the procedure.
1. The Canadian Early and Mid-Trimester Trial Group. Randomized trial to assess safety and fetal outcome of early and midtrimester amniocentesis. Lancet 1998;351:242–7.
2. Reece EA. Early and midtrimester genetic amniocentesis, safety and outcomes. Obstet Gynecol Clin North Am 1997;24:71–81.
3. Galle PC, Meis PJ. Complications of amniocentesis, a review. J Reprod Med 1982;27:149–55.
4. Stark CM, Smith RS, Lagrandeur RM, Batton DG, Lorenz RP. Need for urgent delivery after third-trimester amniocentesis. Obstet Gynecol 2000;95:48–50.
5. Haeusler MC, Konstantiniuk P, Dorfer M, Weiss P. Amniotic fluid insulin testing in gestational diabetes: Safety and acceptance of amniocentesis. Am J Obstet Gynecol 1998;179:917–20.
6. Fleiss J. Statistical methods for rates and proportions. 2nd ed. New York: John Wiley and Sons, 1981.
7. Piiroinen O, Erkkola R, Gronroos M. Low-risk amniocentesis in the third trimester under ultrasound control. Eur J Radiol 1984;4:309–11.
8. Teramo K, Sipinen S. Spontaneous rupture of fetal membranes after amniocentesis. Obstet Gynecol 1978;52:272–5.
9. Gordon HR, Deukmedjian AG. Suprapubic vs. periumbilical amniocentesis. Am J Obstet Gynecol 1975;12:287–90.
10. Anandakumar C, Wong YC, Annapoorna V, Arulkumaran S, Chia D, Bongso A, et al. Amniocentesis and its complications. Aust N Z J Obstet Gynaecol 1992;32:97–9.
© 2002 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.
11. Blessed WB, Lacoste H, Welch RA. Obstetrician-gynecologists performing genetic amniocentesis may be misleading themselves and their patients. Am J Obstet Gynecol 2001;184:1340–4.