Objective To identify and evaluate clinical characteristics in pregnancy leading to stillbirth of both twins.
Material and methods All 68 twin deliveries in Sweden from 1973 to 1989 inclusive, where both twins were dead at birth, were identified by extracting information filed at the Medical Birth Registry (MBR), the National Board of Health and Welfare, Stockholm. Information in the MBR was used for analysis. A questionnaire was also distributed to each delivery unit to obtain information on ultrasound scan made before either or both twins died, and type of placentation.
Results The relative risk for like-sexed (n= 66) vis-à-vis unlike-sexed fetuses (n= 2) to suffer intrauterine death was 12.6 (95% confidence limits 4.3, 375). The rate of like-sexed twins was 97.1%versus 72.2% for the general twin population; monochorionic placentation was identified in 50.0% of these pregnancies. In only seven was there a cause of death evident, including five pregnancies with lethal malformation. The median gestational duration was 33 weeks (range 26 to 41). For the smaller twin in the pair there was an obvious trend toward low birthweight and 16.1% were by definition small for gestational age, whereas the larger twins seemed to have a normal birthweight distribution. The proportion of pregnancies with both twins stillborn increased significantly with increasing discordance in weight (linear trend χ2= 4.5; P= 0.03). The interval between ultrasound examination showing two living fetuses and delivery was nine days or less in half the cases.
Conclusion The major risk factor for fetal deaths seems to be a like-sexed pregnancy with a monochorionic placenta. About half of pregnancies with available information had no more than nine days between an ultrasound examination, confirming two living fetuses, and birth. The great majority of these twins did not show evidence of growth retardation, but birthweight discordance may be a risk factor for fetal death.