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Risk of Fetal Loss in Twin Pregnancies Undergoing Second Trimester Amniocentesis

From the Department of Obstetrics and Gynecology, Hadassah University Hospitals, Ein Karem; and Department of Obstetrics and Gynecology, Hadassah University Hospitals, Mt. Scopus, Jerusalem, Israel.

Address reprint requests to: S. Yagel, MD, Hadassah University Hospital, Mt. Scopus, Department of Obstetrics and Gynecology, PO Box 24035, Jerusalem, Israel; E-mail: syagel{at}hadassah.org.il.

	ABSTRACT

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OBJECTIVE: To assess the rate of fetal loss among bichorionic twin gestations undergoing genetic amniocentesis compared with singletons undergoing the procedure and untested twins.

METHODS: In a retrospective cohort study, three groups were compared: 476 women with twins undergoing amniocentesis, 489 women with singleton gestations undergoing amniocentesis, and 477 women with twins presenting at a similar gestational age for ultrasound studies only. All subjects were scanned at 17–18 weeks’ gestation and again approximately 4 weeks after the procedure or first ultrasound scan. Excluded were twin pregnancies after fetal reduction or chorionic villus sampling, fetuses with structural anomalies, and cases in which one fetus had died at the time of examination or after fetal reduction.

RESULTS: Thirteen twin gestations in the tested group (2.73%) aborted spontaneously up to 4 weeks after the procedure compared with three twin controls (0.63%, P = .01) and three post-procedure singleton controls (0.6%, P = .01). An abnormal karyotype was discovered in 15 tested twin pregnancies (3%) and in six tested singletons (1.23%). All affected twin pairs were discordant for the chromosomal anomaly.

CONCLUSION: The risk of early fetal loss in twins undergoing amniocentesis appears to be higher than that of exposed singletons or unexposed twins.

The frequency of twin pregnancies has increased during the past decade. Because the risk of genetic abnormalities in twins is 1.6 times greater than that in singletons, a substantial number of women carrying twins may be advised to undergo invasive prenatal diagnostic testing. Amniocentesis is the most commonly performed procedure. However, this recommendation needs careful evaluation because of the possible increased risk of amniocentesis-related fetal loss in twin gestations.^1–11

Previous studies evaluating the risk of amniocentesis in twins, which either had inadequate controls or involved only a small number of patients,^8,9 yielded conflicting results. Anderson et al⁸ and Kidd et al⁹ found an increased fetal loss rate among twins undergoing amniocentesis, whereas Ghidini et al¹⁰ did not. Sebire et al¹² suggested that fetal loss in twins undergoing amniocentesis with a single uterine entry may be similar to that of singletons.

To assess the risk of early fetal loss after amniocentesis in twin pregnancies, we retrospectively studied three large cohorts: women with twin pregnancies who underwent amniocentesis, women with twin pregnancies who did not undergo amniocentesis, and women with singleton pregnancies who underwent amniocentesis.

	MATERIALS AND METHODS

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We studied women with bichorionic twin pregnancies who underwent ultrasound scanning at 17–18 weeks’ gestation at the Hadassah University Hospitals in Jerusalem and Ichilov Hospital in Tel-Aviv between 1990 and 1997. This retrospective cohort study included 476 women who underwent amniocentesis and comprised the study group. For controls, we analyzed 477 women with twin pregnancies who underwent ultrasound examination during the same period but not amniocentesis. To compare the fetal loss rate between the patients with twin and singleton pregnancies, we examined an additional cohort of 489 women with singleton pregnancies who underwent amniocentesis during the same gestational weeks. Cohorts were selected in the following manner: all bichorionic twins presenting for genetic amniocentesis on a given day were included, and two singletons recorded from the same daily record, whose procedures were performed by the same physician, were included as controls. Twins presenting for ultrasound scanning only were selected in a similar manner. We excluded twin pregnancies presenting after fetal reduction or chorionic villous sampling, pregnancies in which one or more of the fetuses had structural anomalies, and pregnancies in which one of the fetuses had died at the time of the ultrasound examination. Also excluded were cases in which loss of the pregnancy occurred after selective feticide in twins discordant for chromosomal anomalies.

The ultrasound examination performed at 17–18 weeks’ gestation included a brief anatomy and biometry assessment, including biparietal diameter and head circumference, abdominal circumference, and femoral length. After locating the placenta and membranes, women included in the study group underwent amniocentesis under ultrasonographic guidance. A 20-gauge needle was sequentially inserted into the sacs. Fetal viability was demonstrated after the procedure. A follow-up ultrasound examination at 21–23 weeks’ gestation, approximately 4 weeks after the initial ultrasound examination, was performed in all women in the study. The collected data included maternal and gestational age, obstetric and medical history, and indication for the procedure.

We used the Student t test to compare two nondependent groups for quantitative variables to compare post-procedure loss among the groups. To compare the groups for qualitative variables we used the ² test or the Fisher exact test. A logistic regression model was used to identify characteristics related to postamniocentesis loss.

	RESULTS

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The indications for amniocentesis were compared between the tested groups. A maternal age of at least 35 years was the most common indication (47% of twin gestations and 49% of singletons); followed by an abnormal maternal serum alpha-fetoprotein level (21% and 24%); maternal request (20% and 15%); and ultrasound markers (11% and 12%). In the twin group, slightly less than 1% sought genetic amniocentesis for reasons of family history of genetic disease. None of the women with singletons reported family history as a reason for the procedure. However, the groups differed in that 9% of the twin pregnancies were achieved with fertility treatment compared with 4% of the singletons.

Thirteen twin gestations in the amniocentesis group (2.73%) aborted spontaneously up to 4 weeks after the procedure compared with only three twin controls (0.63%, P = .01) and three postprocedure singleton controls (0.6%, P = .01). None of these were found to have an abnormal karyotype. In all cases in both groups of twins (amniocentesis and control), fetal loss refers to the loss of both fetuses; in our study group, no cases of death of one twin fetus was discovered up to 4 weeks after the procedure. The incidence of fetal loss for all groups is shown in Table 1.

The Student t test and logistic regression analysis revealed that the datum of greatest statistical significance was the number of needle punctures to risk of pregnancy loss (P < .03, odds ratio 0.24, 95% confidence interval 0.068, 0.8). To determine whether prior differences between the groups could account for the higher loss rate in the twin pregnancies, we compared the initial sonographic findings and the findings during amniocentesis between the groups. During the procedure, cloudy fluid (translucent gray to white or yellow in appearance, not green or bloody) was obtained in significantly more twin pairs than in the singleton controls (15 versus 5, P = .012). Two of this subgroup of twin gestations, but none of the affected singletons, were subsequently lost. A significant correlation was found between the cloudy fluid obtained at amniocentesis and an increased incidence of postprocedure fetal loss (P = .035, odds ratio 0.29; confidence interval 0.63, 1.38).

Blood contamination was recorded in 24 twin gestations and 18 singletons, but no relationship between this finding and an increased risk of fetal loss was evident (P = .55). In each of these subgroups (the tested twins and singletons for whom blood contamination of amniotic fluid collected during the procedure was recorded), one case of pregnancy loss occurred up to 4 weeks after the procedure.

To determine whether the initial sonographic findings or later findings during amniocentesis differed significantly among patients who had early fetal loss, we compared these findings between the twin and singleton amniocentesis groups. We did not find a significant effect of maternal age (P = .29), gestational age at amniocentesis (P = .18), the indication for amniocentesis (P = .39), obstetric history (P = .14), or placental location (P = .25) on fetal loss.

	DISCUSSION

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We found a significantly higher loss rate in the twin pregnancies undergoing amniocentesis up to 4 weeks after the procedure compared with the untested control twins and postamniocentesis singletons. We conducted an English-language literature search in the MEDLINE and Medconsult databases for articles published between January 1989 and March 2000, using the terms "amniocentesis" and "twins" initially and then "genetic testing," "fetal loss," "fetal demise," "pregnancy outcome," "multiple," and other variations to expand and then focus the search to glean as many pertinent articles as possible. The searches were repeated (separately) by the first and third authors in an attempt to avoid missing important sources. The search identified no references with as large a study population as ours. Anderson et al⁸ and Pruggmayer et al¹¹ in uncontrolled studies reported a fetal loss rate of 3.57% and 8.1%, respectively, in twin pregnancies undergoing amniocentesis, with a follow-up of up to 28 weeks’ gestation. Kidd et al⁹ in a retrospective cohort study of 227 twin gestations undergoing amniocentesis and 227 twin controls found the rate of stillbirth among exposed pregnancies to be as high as 5.3% and a rate of loss among untested twins of 3.1%. Ghidini et al¹⁰ in a controlled study did not find a significant difference in the fetal loss rate between 101 twin gestations and 108 singleton controls. Ghidini and co-workers¹⁰ studied a smaller group of patients and determined the fetal loss rate up to delivery. As stated above, we determined the loss rate up to 4 weeks after the procedure. Limiting the follow-up to 4 weeks after the procedure may have helped to eliminate background noise from our study and to pinpoint those cases in which the fetal loss was most likely attributable to the amniocentesis.

We compared other characteristics (maternal age, gestational age at amniocentesis, indication for amniocentesis, obstetric history, and placental location) between the study group and singleton controls. Except for the type of fluid obtained (clear, cloudy, or bloody), we did not find any difference between the groups. The cloudy fluid may represent an early event of small abruption of the placenta. Similarly, Plockinger et al¹³ examined more than 2000 procedures retrospectively to determine whether the indications for amniocentesis were risk related to subsequent postprocedural complications and found no differences among the subgroups.

In our study groups, chromosomal abnormalities were found in 1.2 times more twin than singleton fetuses. This is in accordance with the increased risk of chromosomal anomalies in twin pregnancies: for example, a 33-year-old woman carrying twins has the same Down syndrome risk as a 35-year-old woman with a singleton.³

Given the large number of cases in our study and the additional comparison to singleton pregnancies undergoing amniocentesis, we believe that the risk of early fetal loss is apparently higher in twins undergoing amniocentesis than in untested twins or tested singletons. These data can be of value in counseling parents of twins because of the increased number of gestations resulting from fertility programs and the elevated risk of chromosomal abnormalities in twin pregnancies.

	Footnotes

 
We thank Professor Ligom of Ichilov Medical Center for providing data regarding the patients of that center.

PII S0029-7844(01)01416-8

Received August 28, 2000. Received in revised form February 5, 2001. Accepted March 14, 2001.

	REFERENCES

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7. Wapner R. Genetic diagnosis in multiple pregnancies. Semin Perinatol 1995;19:351–62.[Medline]

8. Anderson RL, Goldberg JD, Golbus MS. Prenatal diagnosis in multiple gestation: 20 years experience with amniocentesis. Prenat Diagn 1991;11:263–70.[Medline]

9. Kidd SA, Lancaster PA, Anderson JC, Boogert A, Fisher CC, Robertson R, et al. A cohort study of pregnancy outcome after amniocentesis in twin pregnancy. Paediatr Perinat Epidemiol 1997;11:200–13.[Medline]

10. Ghidini A, Lynch L, Hicks C, Alvarez M, Lockwood CJ. The risk of second trimester amniocentesis in twin gestations: A case-control study. Am J Obstet Gynecol 1993;10: 1013–6.

11. Pruggmayer M, Baumannt P, Schuttei H, Osmerrs R, Bartels I, Jovanovich V, et al. Incidence of abortion after genetic amniocentesis in twin pregnancies. Prenat Diagn 1991;11:637–40.[Medline]

12. Sebire NJ, Noble PL, Odibo A, Malligiannis P, Nicolaides KH. Single uterine entry for genetic amniocentesis in twin pregnancies. Ultrasound Obstet Gynecol 1996;7:26–31.[Medline]

13. Plockinger B, Povse B, Ulm MR, Chalubinski K, Deutinger J, Bernaschek G. [Does the risk of complications after amniocentesis depend on the indications for intervention? An evaluation of 2,066 punctures.] Gegurtshilfe-Frauenheilkd 1996;56:128–31.

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