[Higher order multiple births in Iceland 1982-1998.]

To investigate the incidence of higher order multiple pregnancies in Iceland during the last 17 years.

The incidence of higher order multiple births has been rising in many countries during the last 10-20 years. This increase is mostly due to more successful treatment of infertility. In order to answer the question how the incidence of multiple pregnancies has been during recent years, the following study was undertaken.

Informations about multiple pregnancies were gathered from the records of the Icelandic Birth Registry for the years 1982-1998.

There was a total of 73,164 births during this period, including 960 twins and 34 higher order multiple births (33 triplets and one quadruplets birth). The period was divided into the period prior to and after in vitro fertilisation - IVF. The latter period was then divided into two parts creating three groups with a similar total number of births that was nearly equally divided between these three groups. Twin births were 239, 298 and 423 in each group and the incidence increased from 1:103 to 1:85 and 1:55 as a proportion of total births in each period. The number of higher order multiple births was four, nine and 21 in the three periods giving an incidence of 1:6127, 1:2803 and 1:1116. There was therefore an increase in multiple births during this period and the increase in higher order multiples was greater than for twins. Of the 103 higher order multiple babies born four died, giving a perinatal mortality of 38.8%o. Mean gestational age at birth was 33.3 weeks, ranging from 27 to 37 weeks. All babies were delivered by Cesarean section. The first born baby of the triplets was generally the heaviest one and the last born the lightest. The mean birth weight of the last born was close to -2 standard deviation (SD) as compared with singletons of the same gestational age.

The incidence of multiple births has been increasing in Iceland during the last 17 years and specially during the last decade. The increase is mostly in the era after IVF treatment became more successful.