Delivery for uncomplicated dichorionic twin pregnancies should be considered at 37 weeks’ gestation, a week earlier than is generally recommended in the United States, according to a systematic review and meta-analysis of studies that reported rates of stillbirth and neonatal mortality at various gestational ages.
The researchers assessed the competing risks in twin pregnancies of stillbirth from expectant management versus neonatal death from early delivery, looking for an optimal gestational age at which these risks were balanced.
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In dichorionic pregnancies continuing beyond 34 weeks, these perinatal risks were balanced at 37 weeks. Beyond that, “the risks of stillbirth significantly outweighed the risk of neonatal death from delivery,” with a 1-week delay in delivery (to 38 weeks’ gestation) leading to an additional 8.8 perinatal deaths per 1,000 pregnancies due to an increase in stillbirth, Fiona Cheong-See, MD, of the Queen Mary University of London and her colleagues reported (BMJ 2016;354:i4353. doi: 10.1136/bmj.i4353).
The review included 32 studies published in the past 10 years (observational cohort studies and cohorts nested in randomized studies) that reported rates of stillbirth and/or neonatal outcomes, including neonatal mortality, in monochorionic and/or dichorionic twins. Neonatal death was defined as death up to 28 days after delivery.
The study authors shared unpublished aggregate and individual patient data with the meta-analysis researchers, which enabled an analysis at weekly intervals. The data included in the review covered 35,171 women with twin gestations (29,685 dichorionic and 5,486 monochorionic pregnancies).
Pregnancies with unclear chorionicity, monoamnionity, and twin-to-twin transfusion syndrome were excluded from the analysis.
In monochorionic pregnancies continuing beyond 34 weeks (2,149 pregnancies), there was a trend after 36 weeks toward stillbirth risk being higher than the risk of neonatal death, but the risk difference was not significant.
More data are needed, the researchers said, but “based on our findings, there is no clear evidence to recommend early preterm delivery routinely before 36 weeks in monochorionic pregnancies.”
A committee opinion published by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine (ACOG-SMFM) on medically indicated late-preterm and early-term deliveries states that decisions regarding the timing of delivery should be individualized and should take into account relative maternal and newborn risks, practice environment, and patient preferences (Obstet Gynecol. 2013;121:908-10).
Still, the ACOG-SMFM document offers delivery recommendations: 38 0/7-38 6/7 weeks of gestation for dichorionic-diamniotic pregnancies, and 34 0/7-36 6/7 weeks of gestation for monochorionic-diamniotic pregnancies.
The opinion was published in 2013 and reflects recommendations made 2 years earlier by the National Institute of Child Health and Human Development and SMFM after a workshop on indicated preterm birth (Obstet Gynecol 2011;118:323-33). ACOG and SMFM reaffirmed their document in 2015.
Dr. Brigid McCue
Brigid McCue, MD, chief of ob.gyn. at Beth Israel Deaconess Hospital–Plymouth (Mass.) and a member of ACOG’s Committee on Obstetric Practice, said the meta-analysis is of “high quality,” with “helpful and valid” findings for dichorionic twins.
The risk of stillbirth was 1.2/1,000 pregnancies at 34 weeks’ gestation, while the risk of neonatal death from delivery was 6.7/1,000 pregnancies. The risk of stillbirth remained significantly lower than the risk of neonatal death from delivery at 35 weeks, and was lower at 36 weeks as well. At 37 weeks, the two categories of perinatal death risk were basically balanced, with the risk of stillbirth at 3.4/1,000 pregnancies.
Beyond that, at 38 weeks’ gestation, the risk of stillbirth (10.6/1,000) significantly outweighed the risk of neonatal death from delivery (1.5/1,000) for a pooled risk difference of 8.8.
“The finding that stillbirth risk is higher when you allow someone to go from 37 to 38 weeks – I think this is true,” Dr. McCue said in an interview.
Further research needs to account, however, for the risks of neonatal morbidity at 37 and 38 weeks. “The next question in coming up with a point of inflection is to ask, What are other contributors to the balance of timing of the delivery?” Dr. McCue said. “There’s a bigger picture that needs more analysis.”
“We don’t induce singletons prior to 39 weeks because they can have more respiratory distress, more hypoglycemia, more temperature instability, and less success breastfeeding, for example,” she added. “These complications pale in comparison to a stillbirth, but the numbers of stillbirth are so low and the numbers for [these other morbidities] are much higher.”
The authors of the meta-analysis noted that their findings were limited by the common policy of planned delivery beyond 37 and 38 weeks’ gestation. “This reduced the sample size near term, particularly in monochorionic pregnancies, and could have led to underestimation of risk of stillbirth in the last weeks of pregnancy,” they wrote.