A major study has yielded important information on the optimal timing of delivery of twins and triplets. It suggests that perinatal outcomes could be optimized by the delivery of twins by 39 weeks gestation, and the delivery of triplets by 36 weeks gestation.

Specialists at the Columbia Presbyterian Medical Center, New York, and the University of Colorado, in Denver, USA, hypothesized that prospective fetal risk might be greater in multiple pregnancies, possibly due to an increased risk of uteroplacental insufficiency at advanced gestational ages.

More than 11 million gestations

To investigate, the researchers evaluated the prospective risk of fetal death in singleton, twin and triplet pregnancies, comparing these risks with fetal and neonatal death rates. They analyzed a total of 11,061,599 singleton, 297,622 twin, and 15,375 triplet gestations included in the 1995-1998 birth and death records of the National Center for Health Statistics.

Classic fetal death rates were calculated as the number of fetal deaths as a proportion of total births at a given gestational age, while prospective risk of fetal death was calculated as the number of fetal deaths as a proportion of all fetuses still at risk at a given gestational age: both were expressed as rates per 1,000.

In their paper, published in the latest issue of Obstetrics & Gynecology, the researchers report detailed findings for each week of gestation, from 24 weeks onwards.

Overall, they found that the prospective risk of fetal death was greater for triplets and twins than for singletons, and greater for triplets than for twins, during the third trimester. This pattern ñcorroborates with uteroplacental insufficiency as a suspected underlying mechanism,î say the specialists.

Presented graphically, the prospective risk of fetal death was U-shaped for singletons, twins and triplets, with the risk late in the third trimester greater than at the limits of viability.

Importantly, lines plotting the prospective risk of fetal death and neonatal mortality intersected at approximately 36 weeksÍ gestation for triplets, approximately 39 weeksÍ gestation for twins, and approximately 43 weeksÍ gestation for singletons.

Balancing risks

Concluding, the researchers suggest that delivery might be indicated when the prospective risk of fetal death exceeds the neonatal mortality risk: ñThis data set suggests that it might be reasonable to consider delivery of twins by 39 weeks and triplets by 36 weeks, to improve perinatal outcome.

îThey point out that most triplets are already delivered before 36 weeksÍ gestation ñfor various obstetric reasonsî. However, in the large study sample, a total of 15.8 percent of triplet gestations remained undelivered at 36 weeks. ñAlthough this is a small proportion of triplets, delivery at this point might still result in decreased perinatal mortality for these pregnancies,î say the researchers.

Source: Obstetrics & Gynecology 2003; 102: 685-92
Issue 23: 17 Nov 2003