Dear Sir,

We noted with interest Noar et al's letter of 20th July 2001 describing their as yet unpublished work on outcomes of infants from multiple gestation pregnancies. We look forward to seeing the data and methods of analysis on which their conclusions were based.

We discussed Nielsen et al's work in our paper where we noted that 'the sample size and analytical approach may explain discrepancies with our results'. Nielsen and colleagues investigated 203 infants from multiple gestations and did not take into account the sibling relationship between twin pairs, perhaps explaining their inability to find the significant difference between sibling pairs observed in our series of 602 infants.

Yours sincerely

Doug Hacking
Andrew Watkins
Simon Fraser
Rory Wolfe
Terry Nolan

I read with interest the article by D Hacking et al.
In their article they stress the significantly increased risk of RDS in the second twin. Our experience presented in the study 'Comparative outcome study between triplet and singleton preterm newborns' [1], differ from their findings. Birth order of the triplets did not influence the incidence or severity of Respiratory distress syndrome(RDS), Transient tachypnoea of the newborn, Oxygen therapy at 36 weeks corrected age, Continuous positive airway pressure, Intermittent mandatory ventilation and High frequency ventilation and the Apgar score at one and five minutes. Nielson et al [2] found no significant difference in the incidence of RDS between the first and second born twin.

The literature is controversial. Hacking et al found that the risk of RDS is greater for twins above 29 weeks gestation. Our analysis by three gestational age groups, namely >28weeks, 29–30 weeks and 31–34 weeks yielded no differences for the incidence and severity of RDS or any of the other parameters tested. This relationship held true even when the youngest babies (gestational age >28weeks) were analyzed separately.

In conclusion the outcome of the second twin is still controversial in the literature and a prospective multifactorial study is recommended.

References

(1) Comparative outcome study between triplet and singleton preterm newborns. Maayan-Metzger A, Naor N, and Sirota L (in press)
(2) Neonatal outcome of very premature infants from multiple and singleton gestations. Nielsen H C, Harvey-Wilkes K, MacKinnon B, et al. Am J Obstet Gynecol 1997;177:653-9.