SAN DIEGO (FRONTLINE MEDICAL NEWS)When it comes to reducing the risk of infant death and stillbirth in twin pregnancies, the ideal delivery date is somewhere around 37 weeks’ gestation.

That’s the key finding from a retrospective cohort study using national data that was presented by Dr. Jessica Page at the annual Pregnancy Meeting sponsored by the Society for Maternal-Fetal Medicine.

The study aimed to better characterize the optimal delivery timing in twin pregnancies by quantifying the risk of stillbirth during each week of gestation, along with the risk of infant death following delivery at each week between 32 and 40 weeks.

“There is an existing body of work examining this question in the obstetric literature and debate persists as to the ideal delivery timing,” Dr. Page of the department of obstetrics and gynecology at the University of Utah, Salt Lake City, said in an interview. “This is somewhat difficult to study given the low frequency of twin gestations and rarity of fetal and infant mortality.”

Using nationally linked birth and death certificate data involving 454,625 twin pregnancies from 2006 to 2008, the researchers determined the incidence of stillbirth (defined as fetal death after 20 weeks’ gestation) and infant death (defined as death within the first year of life) for each week of pregnancy from 32 weeks’ through 40 weeks’ and 6 days gestation. Pregnancies complicated by fetal anomalies were excluded from the analysis.

The researchers next estimated the risk associated with continued pregnancy by combining the stillbirth risk during the additional week of pregnancy with the risk of infant death following delivery at the conclusion of that week. This composite risk was compared to the infant death risk associated with delivery at the corresponding gestational age.

Dr. Page and her associates found that the risk of stillbirth increased between 37 and 38 weeks’ gestation (12.5 per 10,000 vs. 22.5 per 10,000, respectively; P less than .05) as well as between 39 and 40 weeks’ gestation. The risk of infant death following delivery gradually decreased as pregnancies approached term gestation with statistically significant decreases in mortality risk with each additional week of pregnancy from 32 through 36 weeks’ gestation.

The composite risk of stillbirth and infant death associated with an additional week of pregnancy had a significant increase from 37 to 38 weeks’ gestation (43.9 per 10,000 vs. 59.2 per 10,000; P less than .05). This rise in fetal/infant death risk continued through 40 weeks’ gestation with significant differences between both 38 and 39 weeks’ and 39 and 40 weeks’ gestation.

“We found that mortality risk was minimized at 37 weeks’ gestation,” Dr. Page said. “This finding corresponds with prior work regarding delivery timing for twins. We did observe a significantly increased risk of mortality following 38 weeks’ gestation due to increased stillbirth risk. However, since we could not control for chorionicity, we cannot make recommendations based solely on these data.”

The study’s main limitation is that chorionicity is not included in birth certificate data and so the researchers were unable to compare monochorionic versus dichorionic pregnancies.

“This is a very important risk factor in the management of twin pregnancies and additional work is needed in this regard,” Dr. Page said. “We additionally could not study specific neonatal morbidities, which also adds to the risk stratification regarding preterm delivery.”

Dr. Page reported having no relevant financial conflicts.

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