Third Trimester Risky for Uncomplicated Monochorionic Twin Pregnancies

The risk of stillbirth in uncomplicated monochorionic twin pregnancies is severalfold higher than that for dichorionic twin pregnancies throughout the third trimester, concluded a systematic review and meta-analysis.¹
   
Compared with dichorionic twin pregnancies, monochorionic twin pregnancies are at greater risk for complications, such as twin-to-twin transfusion syndrome, growth restriction, or major anomalies. However, previous studies have shown that even uncomplicated monochorionic twin pregnancies have an increased risk for late fetal death. The ideal timing of delivery to reduce the risk of death of a co-twin remains unknown, but some experts have recommended delivery of monochorionic-diamniotic twins between 34 and 37 weeks’ gestation.²
   
This latest systematic review and meta-analysis evaluated studies of stillbirth rates specific to gestational age (after 24 weeks’ gestation) in uncomplicated monochorionic-diamniotic twin pregnancies. Calculated in 2-week gestational age blocks, the rate and risk of stillbirth in uncomplicated monochorionic-diamniotic pregnancies were compared with those of dichorionic pregnancies as reported in included controlled studies.
   
The analysis found that for every 1000 uncomplicated monochorionic-diamniotic pregnancies, the rate of stillbirth was 5.1 at 32 to 33 weeks’ gestation, 6.8 at 34 to 35 weeks’ gestation, and 6.2 at 36 to 37 weeks’ gestation. The authors reported that the risk of stillbirth per pregnancy was 1.6% at 32 weeks’ gestation, 1.3% at 34 weeks’ gestation, and 0.9% at 36 weeks’ gestation.
   
At 36 weeks’ gestation, the risk of stillbirth for women with uncomplicated monochorionic-diamniotic pregnancies was more than 8 times that of women with uncomplicated dichorionic pregnancies. An overall comparison showed that the odds ratio for stillbirth per pregnancy for uncomplicated monochorionic-diamniotic pregnancies was 4.2 at 32 weeks’ gestation, 3.7 at 34 weeks’ gestation, and 8.5 at 36 weeks’ gestation.
   
These results strengthen the evidence that supports the recommendation of some experts to offer elective delivery at 34 to 35 weeks’ gestation in uncomplicated monochorionic-diamniotic pregnancies. The 2011 NICHD and SMFM workshop paper on timing of delivery suggested delivery of monochorionic-diamniotic twins between 34 and 37 weeks’ gestation. Some consider this late-preterm/early-term delivery recommendation an aggressive approach, and it does not represent the standard of care.² However, these results do support the use of frequent antenatal testing and ultrasound assessment throughout the third trimester and should be considered in decisions about the timing of delivery in otherwise normal monochorionic-diamniotic twin pregnancies, concluded the authors.¹

Pertinent Points:
- The risk of stillbirth in uncomplicated monochorionic twin pregnancies is substantial throughout the third trimester and is significantly higher than that for dichorionic twin pregnancies.
- Decisions about the timing of delivery in otherwise normal monochorionic twin pregnancies should give serious consideration to the increased risk of fetal death to the co-twin in such pregnancies.
 

References:

1. Danon D, Sekar R, Hack KE, Fisk NM. Increased stillbirth in uncomplicated monochorionic twin pregnancies: a systematic review and meta-analysis. Obstet Gynecol. 2013;121:1318-1326.
2. Newman R, Unal ER. Multiple gestations. In: Gabbe SG, Niebyl JR, Simpson JL, et al, eds. Obstetrics: Normal and Problem Pregnancies. 6th ed. 2012:673-705. Available at: http://www.mdconsult.com/books/page.do?eid=4-u1.0-B978-1-4377-1935-2..00030-2--s0210&isbn=978-1-4377-1935-2&type=bookPage&from=content&uniqId=419322965-2. Accessed July 31, 2013.