Objective
We sought to investigate outcomes of contemporaneously managed monochorionic diamniotic (MCDA) twins, stratified by pregnancy complication.
Study design
Four hundred eighteen MCDA pregnancies from 2001 through 2008 were retrospectively reviewed.
Results
There were 236 ongoing pregnancies at 24 weeks’ gestation. The likelihood of progressing from 24 weeks to 2 live births was 98.7% in uncomplicated pregnancies, 89.7% with twin-twin transfusion syndrome, and 100% with growth discordance, increasing at 32 weeks to 99.5%, 93.8%, and 100%, respectively. The relative risk (RR) of birth <32 weeks was significantly greater in twin-twin transfusion syndrome (RR, 4.1; 95% confidence interval, 2.7–6.1) and growth discordant (RR, 2.1; 95% confidence interval, 1.8–3.8) pregnancies than in uncomplicated pregnancies ( P < .0001).
Conclusion
This represents one of the largest cohorts of MCDA twins. The risk of third-trimester fetal loss was low. The likelihood of both intrauterine fetal demise and preterm birth were greater in complicated pregnancies. In the absence of a clinical indication for delivery, these data do not support elective preterm delivery for prevention of intrauterine fetal demise in uncomplicated MCDA twins.
Outcomes and management of monochorionic diamniotic (MCDA) twin pregnancies have been the subject of much research and speculation over the past decades. While dichorionic diamniotic pregnancies are more common, MCDA pregnancies are affected by a unique set of complications, and therefore have a higher burden of associated morbidity and mortality for both mother and child. In particular, a high rate of delivery in the early preterm period leads to increased neonatal intensive care and costs to the health care system as a whole. Substantial efforts have been made to understand these pregnancies better and improve outcomes; however, the natural history of MCDA pregnancies is far from clear.
Care of uncomplicated MCDA pregnancies remains controversial, with some groups arguing for elective preterm delivery to prevent late intrauterine fetal demise (IUFD). This strategy likely increases the incidence of neonatal complications due to prematurity. Findings specific to neonatal outcomes of MCDA pregnancies are mixed; some studies argue that neonatal morbidity and mortality in all twin pregnancies may nadir at 37 weeks, while 1 recent publication suggests increased neonatal intensive care unit admissions in MCDA compared to dichorionic diamniotic twins at term. We reviewed our own experience with 418 MCDA twins over an 8-year period, with the aim of investigating the optimal timing of delivery of uncomplicated MCDA pregnancies.
As a secondary goal, we sought to improve understanding of the differences between pregnancy outcomes in uncomplicated MCDA pregnancies as compared with those affected by twin-twin transfusion syndrome (TTTS), or by severe growth discordance, to improve antepartum management and patient counseling.
Materials and Methods
This study protocol was approved by our institutional review board. We reviewed the records of all women with MCDA twin pregnancy identified by ultrasound at our hospital from 2001 through 2008. To meet inclusion criteria, all women had a viable MCDA twin pregnancy at ≥14 weeks’ gestation. Five patients with twin reversed arterial perfusion sequence were excluded, as were triplets and twins resulting from selective reduction of higher order multiples. Data collection included pregnancy outcomes, sonographic findings, gestational age at delivery, birthweight, and neonatal survival to hospital discharge. Pregnancy loss rates included all spontaneous IUFD, as well as those resulting from treatment by cord ligation, and cases complicated by preterm premature rupture of membranes (PPROM), preterm labor, or cervical incompetence <24 weeks’ gestation. Very preterm birth was defined as delivery >24 weeks but <32 weeks’ gestation.
All women received some portion of their care at our hospital, where ultrasounds were performed. For retrospective analysis based on ultrasound findings and birthweight, ongoing twin pregnancies at 24 weeks’ gestation were classified into 3 categories as defined below: (1) TTTS; (2) severe growth discordance; and (3) uncomplicated. Minimal fetal surveillance included ultrasound every second week to assess fetal growth and amniotic fluid volume. Umbilical artery Doppler was routinely performed in later years if growth or amniotic fluid discordance was identified. All patients underwent nonstress test or biophysical profile weekly from 32 weeks onward, with additional fetal evaluation determined by the provider. Uncomplicated patients were typically delivered between 35-37 weeks.
The diagnosis of TTTS was made based on discrepancies in amniotic fluid volume, and staging was done according to the Quintero system. Amnioreduction and umbilical cord ligation were offered at our institution, and patients considered to be candidates for laser ablation of the placental bed were referred to an outside facility. Severe growth discordance was defined as a 25% difference in twin birthweights in the absence of TTTS. For 21 cases (6%) where birthweight was unavailable and 7 cases where a single IUFD occurred, estimated fetal weights at the last available ultrasound were substituted. Uncomplicated pregnancies were defined as those with nonanomalous twin infants with concordant birthweights and no ultrasonic evidence of TTTS.
The t test was used to examine differences in the mean gestational age at delivery among uncomplicated, TTTS, and growth discordant twin pregnancies, while the distribution of births in each of these groups <32 weeks and >32 weeks was examined in contingency tables with the χ 2 test. The Fisher’s exact test was also used to compare IUFD rates in the current study to those in the literature.
Results
In the 8-year study period, 418 MCDA twin pairs underwent ultrasound evaluation at ≥14 weeks’ gestation at our hospital. There were 345 ongoing pregnancies at 24 weeks’ gestation with complete delivery data available for 322 (93%). Of these, 13 had a single IUFD <24 weeks, therefore 309 women were included in analyses of ongoing twin pregnancies at 24 weeks’ gestation. Of the remaining 73 pregnancies, 58 were not followed up >24 weeks’ gestation, and 15 had major anomalies in 1 twin and were assessed separately ( Figure 1 ).
The prospective risk of IUFD from 24 weeks onward was 2.3%, and from 32 weeks, 1.6%, when the entire cohort was assessed ( Table 1 ). By comparison, at 24 gestational weeks, 234 (68%) ongoing pregnancies were uncomplicated by either severe growth discordance or TTTS. In this group, the risk of IUFD >24 weeks was 1.3%; unchanged at 28 weeks; and at 32 weeks, 0.5% ( Table 1 ). There were a total of 1 single and 2 double IUFDs in the uncomplicated MCDA pregnancies >24 weeks. The first was a single loss at 33 weeks in a patient with sudden-onset severe preeclampsia, and the second a double IUFD at 31 weeks in the setting of 20% growth discordance. The final patient had symmetrically grown twins with normal fluid and a double IUFD at 26 weeks. In 15 cases with loss of a single twin, including 5 after cord ligation, pregnancy proceeded to result in 1 live birth, with a mean gestational age at delivery of 36 weeks. The surviving twin gained an average of 11 weeks after the demise of the co-twin (range, 0–21).
| Variable | At 24 wk | At 28 wk | At 32 wk |
|---|---|---|---|
| Cohort (n = 309) | n = 309 | n = 291 | n = 245 |
| 2 live births | 97.7% | 98.1% | 99.2% |
| 1 live birth | 1.9% | 1.9% | 0.8% |
| Uncomplicated pregnancy (n = 234) | n = 234 | n = 225 | n = 201 |
| 2 live births | 98.7% | 99.1% | 99.5% |
| 1 live birth | 0.9% | 0.9% | 0.5% |
| Twin-twin transfusion syndrome (n = 39) | n = 39 | n = 32 | n = 16 |
| 2 live births | 89.7% | 90.6% | 93.8% |
| 1 live birth | 10.3% | 9.4% | 6.3% |
| Severe growth discordance (n = 36) | n = 36 | n = 36 | n = 25 |
| 2 live births | 100.0% | 100.0% | 100.0% |
| 1 live birth | 0.0% | 0.0% | 0.0% |
We compared rates of prematurity among uncomplicated MCDA pregnancies to those with TTTS or growth discordance alone ( Table 2 ). Overall, 59% (182) of patients with MCDA pregnancies delivered <37 weeks’ gestation. The mean gestational age at delivery was significantly lower in both TTTS (32 weeks) and growth discordant (33 weeks) groups compared with uncomplicated pregnancies (35 weeks) ( P < .0001), and rates of very preterm birth also differed by subgroup. Both TTTS ( P < .0001) and growth discordant ( P < .02) groups were significantly more likely to deliver <32 weeks than were uncomplicated pregnancies. In uncomplicated MCDA pregnancies, 14% (33) delivered <32 weeks, and 49% (116) delivered ≥37 weeks (term) as compared to TTTS pregnancies, where 59% (23) delivered <32 weeks, and 13% (5) at term (relative risk, 4.1; 95% confidence interval, 2.7–6.1). In those with severe growth discordance, 31% (11) delivered <32 weeks, and 17% (6) at term (relative risk, 2.1; 95% confidence interval, 1.8–3.8) ( Figure 2 and Table 2 ).
