Exploring the safety and diagnostic utility of amniocentesis after 24 weeks of gestation: a retrospective analysis

Introduction

Amniocentesis is a prenatal diagnostic technique that involves the removal of a small amount of amniotic fluid surrounding the fetus [1]. The analysis can include karyotype testing, chromosomal microarray analysis (CMA), whole exome sequencing (WES), or screening for fetal infections. Traditionally, amniocentesis is performed between 15 and 24 weeks of gestation, and most of the available data on its safety, effectiveness, diagnostic capabilities, complications, and patient acceptance pertains to this timeframe.

A recent study by Drukker et al. showed that 11.4 % of all fetal anomalies (3.1 %, or 474 out of 15,244 cases) may only become detectable in a later ultrasound, even if a fetal anomaly scan conducted before 24 weeks was normal [2]. This could necessitate invasive prenatal testing to obtain a definitive diagnosis. Although limited information is available on amniocentesis after 24 weeks, the existing data shows promise.

Considering that the medical termination of pregnancy has been legalized in India for cases with severe fetal abnormalities even beyond 24 weeks, amniocentesis after 24 weeks could offer pregnant women and their families crucial additional information for making informed decisions about various reproductive outcomes [3]. This retrospective analysis aims to provide comprehensive data on amniocentesis beyond 24 weeks, including its indications, complication rate, safety profile, yield, and detailed maternal-fetal outcomes.

Materials and methods

We conducted a retrospective analysis from March 2021 to June 2023 for pregnant women who underwent amniocentesis after 24 weeks at a tertiary care referral center, after obtaining ethical clearance. Fetal medicine specialists performed these procedures. The specialists work in a high-load centre with extensive experience in performing diagnostic and therapeutic prenatal procedures performing more than 100 cases in a month with almost 80 being diagnostic procedures and have shared their experience at various national and international platforms [4], 5]. The method involved a needle puncture to access the amniotic cavity through the patient’s abdomen under ultrasound guidance and using aseptic precautions, followed by the aspiration of amniotic fluid. All procedures were performed as office procedures. Fetal cardiac activity was checked post-procedure for all. Appropriate genetic testing was carried out from amniotic fluid sample.

Additionally, every patient received both pre-test and post-test counseling. Information was obtained from medical records, and patients who did not deliver at our hospital were contacted telephonically regarding their pregnancy outcomes. Pregnant women who were lost to follow-up were excluded from the analysis. Descriptive data was collected on patient demographics, indications for amniocentesis, and the test results. The outcomes analyzed were the complication rates and pregnancy outcomes.

Results

From March 2021 to June 2023, 60 pregnant women with 61 fetuses (one twin pregnancy) underwent amniocentesis at our institute at or beyond 24 weeks. The median age of the pregnant females was 32 years (25–35). The average gestational age at the time of the procedure was 25^4/7 (24^1/7–33^1/7). Thirty-nine women were primigravidas (65 %), whereas 21 were multigravidas (35 %).

The most common indication for amniocentesis was the presence of abnormal sonographic findings, accounting for 72.13 % (44/61) of the procedures. Structural anomalies on USG, accounted for most cases (21/61, 34.42 %). The various indications are listed in Tables 1 and 2. There were no documented complications such as fetal loss, amniotic fluid leakage, chorioamnionitis, or needle injuries observed during the amniocentesis procedures or within the two-week follow-up period after that. There were three culture failures for karyotyping (3/61, 4.91 %), attributed to faulty laboratory supplies at that time and not to the advanced gestational age during testing. Karyotyping was performed on 56 out of 61 samples (91.8 %), targeted gene sequencing on six samples (9.83 %), CMA on five samples (8.19 %), and WES on four samples (6.55 %) (Table 3). Out of the 71 tests done, 67 (94.36 %) yielded normal genetic test results, while 4/71 (5.63 %) had abnormal results indicating potential abnormalities (Table 4).

With regards to the pregnancy outcomes (Table 5), five patients opted for termination of pregnancy along with amniocentesis before the receiving results of the test, and two patients chose to terminate the pregnancy after receiving the genetic test results. The five MTPs done along with genetic testing were for early onset growth restriction, congenital complex heart disease (transposition of great arteries with bicuspid aortic valves and ventricular septal defect), ventriculomegaly, liver calcification along with high risk of trisomy 21 and non-immune hydrops done at 24, 24^1/7, 24^2/7, 32^1/7 and 26^5/7 respectively. All these patients opted for only karyotyping, which was normal. Two terminations were done after reports for Trisomy 21 and Beta glucosidase deficiency at 27 weeks and 32^5/7 weeks respectively. The decision to allow MTP was made after the medical board’s opinion as per the MTP Act and rules [6]. However, one patient was diagnosed with a balanced translocation with normal parent karyotype. The baby delivered prematurely at 33^5/7 weeks and was diagnosed with metabolic syndrome and expired at 3rd month of life. There were two cases of intrauterine demise (IUD). In the first case, amniocentesis was performed at 26 weeks, revealing trisomy 18. Post counseling, the patient chose to continue the pregnancy, but an IUD was detected at 30 weeks. In the second case, amniocentesis was conducted at 24 weeks for a single ventricle. Karyotyping was performed, and results were normal, but IUD was detected at 28 weeks, four weeks after the procedure. Of the 51 remaining pregnancies, there were three preterm deliveries (5.88 %). The prematurity of these two cases, however, cannot be attributed to the procedure as one pregnancy was terminated prematurely for the fetal indication (reversal of end-diastolic flow), and the other two patients went into preterm labor after four weeks of the procedure at 32 and 34 weeks respectively. Out of the 51 pregnant women who continued pregnancy, there were 39 vaginal deliveries (76.47 %; 39/51), and 12 patients (23.52 %; 12/51) required cesarean sections. There were five neonatal and infant deaths (5/51; 9.80 %) (Table 6).

Discussion

In our study, the most frequent indication for amniocentesis beyond 24 weeks was the presence of abnormal sonographic findings. Other indications included positive serum screening, a history of previous babies with identified genetic abnormalities, and early onset fetal growth restriction. Amniocentesis emerged as a valuable option for pregnant women who presented to our center later in their pregnancies due to various reasons, such as delayed identification of anomalies on USG or a lack of awareness about available testing options.

Four (6.55 %) had abnormal results among the patients who underwent late amniocentesis. This is comparable to findings in previous studies, such as Li et al. at 10 % [6], Geffen et al. at 3 % [7], and Daum et al. at 6 % [8]. The 2021 amendment to the Medical Termination of Pregnancy (MTP) bill of India has removed the limit on abortion in cases of significant fetal abnormalities [3]. Before this amendment, even if the anomalies were life-threatening, families had no choice but to continue the pregnancy past 20 weeks. The amendment to the MTP bill has brought tremendous relief to families who require abortions after 20 weeks due to significant fetal abnormalities [3]. In our center, we had two patients who were able to opt for medical termination of pregnancy (MTP) after receiving positive genetic reports indicating anomalies at 26^3/4 and 32^5/7 weeks of gestation and five patients opted for MTP along with the testing. These abortions were safely performed under close monitoring with no complications.

Regarding complications related to amniocentesis, our study did not report any cases of chorioamnionitis, rupture of membranes or needle injuries. We observed three cases of preterm births. Notably, two of these preterm deliveries (twin pregnancies) were planned terminations due to REDF. The remaining preterm delivery occurred four weeks after the procedure. Consequently, the preterm delivery rate in our study was 5 %, which was comparable to rates reported in other studies, such as Li et al. at 2.5 % [6], Geffen et al. at 6 % [7] Gabbay et al. at 9 % [9], and H. Daum et al. at 5 % [8]. A similar study reported from India by Sharma et al. showed that the total yield of positive findings was 14.60 % (22/150; excluding 2 VOUS and amongst all the deliveries, 2.1 % delivered spontaneously within a week of the procedure and about 5.4 % delivered spontaneously within a month of the procedure [10]. Traditionally, failure of amniocyte culture is reported after 0.1 % of procedures. Blood-stained amniotic fluid and late gestational age at amniocentesis increase the risk of culture failure [11]. O’Donoghue et al. reported culture failure rates of 9.7 % in their study of amniocentesis done in the third trimester of pregnancy [12]. Our study reported three culture failures (4.91 %) but all three tests were done in the same week and the failure was due to equipment malfunction and not due to the advances gestational age at testing. In these three cases, common aneuploidies of chromosomes 13, 18 and 21 and sex chromosomes was ruled out by QF-PCR. In a recent systematic review and metanalysis on obstetric outcomes after amniocentesis on singleton pregnancies after 24 weeks of gestation which included five studies, The overall incidence of preterm birth <37 weeks was 4.85 % (95 % CI 3.48–6.56; I² 0.00 %), while preterm within 1 week of amniocentesis was 1.42 % (95 % CI 0.66–2.45; I² 0.00 %). The incidence of placental abruption was 0.91 % (95 % CI 0.16–2.25; I² 0.00 %), the rate of intrauterine fetal demise was 3.66 % (95 % CI 0.00–14.04; I² 90.96 %) and the rate of termination of pregnancy was 6.37 % (95 % CI 1.05–15.72; I² 94.30 %) [13].

Conclusions

Amniocentesis, even at a later gestation, appears to be a safe and effective tool for prenatal diagnosis and provides an opportunity to counsel the couple about various reproductive options, especially as the new MTP bill amendments, allows late MTPs.