Objective
The purpose of this study was to evaluate neonatal outcome of monochorionic twin pregnancies complicated by twin anemia-polycythemia sequence (TAPS).
Study Design
A cohort of consecutive monochorionic twins with TAPS with double survivors was included in the study. Each twin pair with TAPS was compared with 2 monochorionic twin pairs who were unaffected by TAPS or twin-to-twin transfusion syndrome and who were matched for gestational age at birth. Neonatal death, severe morbidity, and cerebral injury were studied.
Results
We included 19 twin pairs in the TAPS group and 38 control twin pairs. The incidence of neonatal death and severe neonatal morbidity was similar in the TAPS group and control group (3% [1/38] vs 1% [1/76] and 24% [9/38] vs 28% [21/76], respectively). Severe cerebral injury was detected in 1 infant (5%) in the TAPS group and 1 infant (2%) in the control group.
Conclusion
Neonatal mortality and morbidity rates in a select population of TAPS neonates are similar to control neonatal rates.
Fetofetal blood transfusion occurs in all monochorionic twins because of the invariable presence of placental vascular anastomoses and can lead to severe complications. The best-known clinical syndrome is twin-twin transfusion syndrome (TTTS). TTTS is characterized by the presence of oligohydramnios in the donor and polyhydramnios in the recipient twin, the so-called twin oligopolyhydramnios sequence (TOPS). Recently, we described a new atypical form of chronic fetofetal blood transfusion, termed twin anemia-polycythemia sequence (TAPS). TAPS is characterized by the presence of large intertwin hemoglobin difference without the degree of amniotic fluid discordance (TOPS) that is required for the diagnosis of TTTS. TAPS may occur after laser surgery for TTTS (post–laser surgery form) in up to 13% of cases. In these post–laser surgery TAPS cases, it is usually the former recipient who becomes anemic, whereas the former donor becomes polycythemic. TAPS may also occur in approximately 3-5% of “uncomplicated” monochorionic twin pregnancies (spontaneous form).
Both spontaneous and post–laser surgery TAPS have a similar anatomic substrate that is based on the presence of only few minuscule arteriovenous placental vascular anastomoses, in the absence of superficial arterioarterial anastomoses. These few minuscule arteriovenous anastomoses lead to a slow, chronic intertwin blood transfusion that allows more time for hemodynamic compensatory mechanisms and may prevent dysregulation of hormonal systems and the development of TOPS.
TAPS can be diagnosed antenatally with predefined Doppler-ultrasound criteria or postnatally with hematologic criteria in combination with placental injection studies. Postnatal diagnosis of TAPS is based on the presence of chronic anemia (with highly increased reticulocyte count) in the donor and polycythemia in the recipient in association with typical placental angioarchitecture after injection with colored dye.
Various studies have shown that monochorionic twins with TTTS have an increased risk for neonatal morbidity, cerebral injury, and neurodevelopment impairment. Whether monochorionic twins with TAPS are also at risk for increased short-term neonatal morbidity or long-term neurodevelopment impairment is not known. To date, outcome in TAPS is based on few case reports. We hypothesized that neonatal morbidity TAPS cases with double survivors is limited mainly to short-term hematologic complications without other severe complications. The aim of this study was to determine the neonatal outcome in a large series of neonates with TAPS in comparison with a control group of monochorionic twins without TAPS.
Materials and Methods
All consecutive monochorionic twin pairs with TAPS who were admitted to our neonatal nursery at the Leiden University Medical Centre (The Netherlands) between June 2002 and February 2009 were included in the study. Our center is an academic referral center that manages all types of complications of monochorionic pregnancies and the national center for invasive fetal therapy. Absence of antenatal signs of TOPS is an absolute and fundamental condition for the diagnosis of TAPS.
For the purpose of this study, definitive diagnosis of TAPS was based on postnatal criteria. Postnatal criteria were met if hematologic investigations at birth showed chronic anemia in the donor (hemoglobin, <5th percentile) and polycythemia in the recipient (hematocrit, >65%) in combination with placental injection studies that showed only small arteriovenous anastomoses (diameter, <1 mm) and no superficial arterioarterial anastomoses. We excluded all twin pregnancies with single or double intrauterine death and cases with an incomplete placental injection study. TAPS cases (whether spontaneous or post–laser surgery TAPS cases) who were treated subsequently with fetoscopic laser surgery were excluded from the study.
Details on the technique that has been used for placental injection and placental territory measurement have been described previously. Part of the placental data reported in this study were included in a previous report on placental angioarchitecture in TAPS. Two spontaneous TAPS cases and 2 post–laser surgery TAPS cases were published previously.
Each twin pair with TAPS was compared with 2 control monochorionic twin pairs who were unaffected by TAPS or TTTS and matched by gestational age at birth (± 1 week gestation).
We recorded the gestational age at birth, birthweight, and intertwin birthweight discordance. Gestational age at delivery was assigned by ultrasound dating during the first trimester.
Hemoglobin levels and reticulocyte count were measured routinely at birth in all monochorionic twins. Blood samplings were obtained primarily from umbilical cord blood. If cord blood was not available, samplings were obtained routinely on day 1 through heel stick or venous puncture. Anemia at birth was defined as a hemoglobin level at <5th percentile for gestational age. Polycythemia-hyperviscosity syndrome was defined as a hematocrit level of >65%. Criteria for blood transfusion and partial exchange transfusion remained unchanged during the study period.
Cranial ultrasound scans were performed in all neonates according to our unit protocol, which requires a minimum of 3 scans during the first week of life (days 1, 3, and 7), followed by weekly scans thereafter until discharge or transfer to another hospital. Intraventricular hemorrhage with or without parenchymal involvement was graded according to the classification of Volpe, and periventricular leukomalacia was graded according to the classification of de Vries et al. Ventricular dilation was diagnosed when measurement of the lateral ventricles exceeded the 97th percentile, with the use of ventricular index measurements as described by Levene. Severe cerebral lesions on ultrasound scans were defined as the presence of at least 1 of the following findings: intraventricular hemorrhage grade III, intraventricular hemorrhage with parenchymal involvement, cystic periventricular leukomalacia ≥ grade II, ventricular dilation, porencephalic or parenchymal cysts, or other severe cerebral lesions that were associated with adverse neurologic outcome. We recorded the following neonatal morbidity: respiratory distress syndrome, chronic lung disease defined as oxygen dependency at 36 weeks postmenstrual age, symptomatic patent ductus arteriosus that required medical therapy or surgical closure, necrotizing enterocolitis of stage II or more, and retinopathy of prematurity of stage III or more. Liver and/or renal function tests were performed in case of clinical suspicion for liver or renal complications. Similarly, echocardiography was not performed routinely, only based on clinical suspicion for cardiac anomaly.
Primary outcome was a composite outcome measure, termed severe neonatal morbidity and defined as any of the following: respiratory distress syndrome, chronic lung disease, patent ductus arteriosus, necrotizing enterocolitis of stage II or more, retinopathy of prematurity of stage III or more, or severe cerebral lesions. Because of the retrospective and observational nature of this study, our local ethical committee stated that the study was exempt from institutional review board approval, according to Dutch legislation.
Clinical characteristics and neonatal outcome were compared between the TAPS and control group. Results of categoric variables were compared with the use of Fisher’s exact test. Normally distributed continuous variables were analyzed with the unpaired Student t test. A probability value of < .05 was considered to indicate statistical significance. Analysis was performed with SPSS software (version 16; SPSS Inc, Chicago, IL).
Results
During the study period, 244 TTTS cases were treated with fetoscopic laser surgery at our center. Single or double fetal death after laser surgery occurred in 55 (23%) and 32 (13%) TTTS pregnancies, respectively. In the remaining 157 TTTS pregnancies with double survival at birth, 15 cases (10%) fulfilled the postnatal criteria of TAPS and were included in this study. One post–laser surgery TAPS case was excluded because of the presence of a (small) superficial arterioarterial anastomosis on placental injection. During the same study period, 152 uncomplicated monochorionic twins were born at our center. Five twin pairs (3%) fulfilled the postnatal criteria for TAPS. Two spontaneous TAPS cases that were detected antenatally were treated with fetoscopic laser surgery after diagnosis and were excluded from the study. In total, 19 consecutive twin pairs fulfilled the criteria for TAPS and were included in the study. Fourteen cases (74%) were post–laser surgery TAPS, and 5 cases (26%) were spontaneous TAPS cases.
Doppler measurements of the middle cerebral artery-peak systolic flow velocity from both fetuses were available from 79% of cases (15/19) in the TAPS group. Increased middle cerebral artery-peak systolic flow velocity in the donor in combination with a decreased middle cerebral artery-peak systolic flow velocity in the recipient was detected antenatally in 60% of these cases (9/15). The mean gestational age at laser surgery in the 14 cases of post–laser surgery TAPS cases was 20.0 weeks (SD, 3.9 weeks). The mean gestational age at detection of TAPS in the 9 antenatally detected post–laser surgery TAPS cases was 25.0 weeks. In 10 of the 14 postlaser surgery TAPS cases (71%), the former recipient was anemic at birth (ie, had become the new donor after laser surgery).
Baseline characteristics in the group with and without TAPS are presented in Table 1 .
| Characteristic | Group | |
|---|---|---|
| Twin anemia-polycythemia sequence (pregnancies, 19; neonates, 38) | Control (pregnancies, 38 pregnancies; neonates, 76) | |
| Gestational age at birth, wk a | 32 ± 2.8 (26–36) | 32.2 ± 2.7 (26–36) |
| Female, n (%) | 16 (42) | 40 (53) |
| Vaginal delivery, n (%) | 10 (53) | 18 (47) |
| Birthweight, gb | 1591 ± 415 | 1780 ± 521 |
| Birthweight discordance, % b | 14 ± 14 | 15 ± 14 |
| Small for gestational age, n (%) | 2 (5) | 4 (5) |
| Placenta with only small arteriovenous anastomoses, n (%) c | 19 (100) | 0 |
| Placenta with arterioarterial anastomoses, n (%) c | 0 | 36 (95%) |
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