New research suggests that, with close fetal surveillance, perinatal morbidity can be minimized by allowing uncomplicated monochorionic pregnancies to go to 37 weeks of gestation before planned delivery and dichorionic twins to 38 weeks.
However, among monochorionic twins, this approach must be balanced against a 1.5% risk of late in utero death, the study team notes in the January 2012 issue of Obstetrics and Gynecology.
To investigate optimum timing for planned delivery of uncomplicated twin pregnancies, Dr. Fionnuala Breathnach, of the Royal College of Surgeons in Ireland, Dublin, studied 1,028 women with twin pregnancies from eight centers in Ireland.
They compared perinatal mortality and a composite measure of perinatal morbidity between uncomplicated twins that underwent planned preterm delivery with monochorionic twins that continued in utero beyond 34 weeks of gestation, and dichorionic twins who continued beyond 36 weeks.
For perinatal morbidity, the researchers chose a composite of respiratory distress, necrotizing enterocolitis, hypoxic ischemic encephalopathy, periventricular leukomalacia, or sepsis.
The researchers had complete perinatal outcome data beyond 28 days of life for 1,001 twin pairs (200 monochorionic and 801 dichorionic). Overall mortality and morbidity in this twin cohort was “remarkably low,” the authors note.
In monochorionic twins, the perinatal mortality rate was 30 per 1,000 total births.
The researchers note that the motivation for elective preterm delivery of monochorionic twins is to eliminate the risk of unanticipated in utero fetal death at a later gestational age. Their study, they say, quantifies that risk at 1.5% at 34 weeks of gestation and 1.7% at 35 weeks of gestation.
“Although elective delivery at 34 or 35 weeks abolishes that specific risk, that decision incurs a cost of neonatal morbidity that translates into an 88% NICU admission rate at 34 weeks, falling to 9% at 38 weeks,” the authors report.
In terms of the composite measure of perinatal morbidity, for uncomplicated monochorionic twins, the risk fell from 41% with delivery at 34 weeks to 5% with delivery at 37 weeks.
In dichorionic twins, the perinatal mortality rate was 3.8 per 1,000. In dichorionic twins undergoing close fetal surveillance, the risk of in utero death after 33 weeks “appears to be almost negligible,” the authors say.
Among dichorionic twins, the risk of morbidity fell from 4% with delivery at 36 weeks to 1% in pregnancies continuing to 38 weeks.
Summing up, Dr. Breathnach and colleagues say picking the optimal time for delivery for both monochorionic and dichorionic twin pregnancies involves not just considering the risk of in utero death, but acknowledging the “dynamic balance” that exists between in utero (fetal) risk and ex-utero (neonatal) risk.
Considering these dynamic risks should help parents make more informed decisions when balancing the risks and benefits of elective preterm delivery, they say.
Obstet Gynecol. 2012;119:50-59.