Objective: To examine the effect of twin-to-twin delivery interval on the umbilical cord blood gas status of the second twin following vaginal delivery.
Design: A retrospective study.
Setting: The department of obstetrics and gynaecology in a university teaching hospital.
Population: Twin deliveries at or beyond 34 weeks of gestation over a period of five years, with the first twin delivered vaginally. Twins with any antepartum complications including discordant growth, intrauterine growth restriction, intrauterine death, fetal malformations and pre-eclampsia were excluded.
Methods: The correlation between the twin-to-twin delivery interval, and both the umbilical arterial and venous blood gas parameters of the second twin, including pH, partial pressure of CO2 and base excess, were studied.
Results: A total of 118 cases were reviewed. The mean gestation at delivery was 37.1 weeks. The median twin-to-twin delivery interval was 16.5 minutes. There were significant negative correlations between twin-to-twin delivery interval and both the umbilical cord arterial and venous pH and base excess of the second twin (P <0.05). There were also significant positive correlations between both arterial and venous partial pressure of CO2 and the delivery interval (P <0.05). Similar changes were found even if the analyses were limited to those who had normal vaginal deliveries. The umbilical arterial pH of Twin 2 was <7.00 in none of the cases delivered within 15 minutes of the birth of Twin 1, 5.9% if within 16-30 minutes, and 27% if more than 30 minutes. Among those with an inter-twin delivery interval of more than 30 minutes, 73% had cardiotocographic evidence of fetal distress which required operative delivery.
Conclusions: Umbilical cord arterial and venous values of pH, partial pressure of CO2 and base excess of the second twin deteriorate with increasing twin-to-twin delivery interval. Risks of fetal distress and acidosis in the second twin are high when the twin-to-twin delivery interval is beyond 30 minutes.